MED SERVICE

                          BY MURRAY LEINSTER

                       Illustrated by van Dongen

           [Transcriber's Note: This etext was produced from
                Astounding Science Fiction August 1957.
         Extensive research did not uncover any evidence that
         the U.S. copyright on this publication was renewed.]



                                   I

    "The probability of unfavorable consequences cannot be zero in any
    action of common life, but the probability increases by a very high
    power as a series of actions is lengthened. The effect of moral
    considerations, in conduct, may be stated to be a mathematically
    verifiable reduction in the number of unfavorable possible chance
    happenings. Of course, whether this process is termed the
    intelligent use of probability, or ethics, or piety, makes no
    difference in the fact. It is the method by which unfavorable chance
    happenings are made least probable. Arbitrary actions such as we
    call criminal cannot ever be justified by mathematics. For
    example ..."

                                        _Probability and Human Conduct_
                                                             Fitzgerald


Calhoun lay in his bunk and read Fitzgerald on "Probability and Human
Conduct" as the little Med Ship floated in overdrive. In overdrive
travel there is nothing to do but pass the time away. Murgatroyd, the
_tormal_, slept curled up in a ball in one corner of the small ship's
cabin. His tail was meticulously curled about his nose. The ship's
lights burned steadily. There were those small random noises which
have to be provided to keep a man sane in the dead stillness of a ship
traveling at thirty times the speed of light. Calhoun turned a page and
yawned.

Something stirred somewhere. There was a click, and a taped voice said:

"_When the tone sounds, break-out will be five seconds off._"

A metronomic ticking, grave and deliberate, resounded in the stillness.
Calhoun heaved himself up from the bunk and marked his place in the
book. He moved to and seated himself in the control chair and fastened
the safety belt. He said:

"Murgatroyd! Hark, hark the lark in Heaven's something-or-other doth
sing. Wake up and comb your whiskers. We're getting there."

Murgatroyd opened one eye and saw Calhoun in the pilot's chair. He
uncurled himself and padded to a place where there was something to
grab hold of. He regarded Calhoun with bright eyes.

"_BONG!_" said the tape. It counted down.
"Five--four--three--two--one--"

It stopped. The ship popped out of overdrive. The sensation was
unmistakable. Calhoun's stomach seemed to turn over twice, and he had
a sickish feeling of spiraling dizzily in what was somehow a cone. He
swallowed. Murgatroyd made gulping noises. Outside, everything changed.

The sun Maris blazed silently in emptiness off to port. The Cetis
star-cluster was astern, and the light by which it could be seen had
traveled for many years to reach here, though Calhoun had left Med
Headquarters only three weeks before. The third planet of Maris swung
splendidly in its orbit. Calhoun checked, and nodded in satisfaction.
He spoke over his shoulder to Murgatroyd.

"We're here, all right."

"_Chee!_" shrilled Murgatroyd.

He uncoiled his tail from about a cabinet-handle and hopped up to look
at the vision-screen. What he saw, of course, meant nothing to him. But
all _tormals_ imitate the actions of human beings, as parrots imitate
their speech. He blinked wisely at the screen and turned his eyes to
Calhoun.

"It's Maris III," Calhoun told him, "and pretty close. It's a colony
of Dettra Two. One city was reported started two Earth-years ago. It
should just about be colonized now."

"_Chee-chee!_" shrilled Murgatroyd.

"So get out of the way," commanded Calhoun. "We'll make our approach
and I'll tell 'em we're here."

He made a standard approach on interplanetary drive. Naturally, it was
a long process. But after some hours he flipped over the call-switch
and made the usual identification and landing request.

"Med Ship _Aesclipus Twenty_ to ground," he said into the transmitter.
"Requesting co-ordinates for landing. Our mass is fifty tons. Repeat,
five-oh tons. Purpose of landing, planetary health inspection."

He relaxed. This job ought to be purest routine. There was a landing
grid in the spaceport city on Maris III. From its control room
instructions should be sent, indicating a position some five planetary
diameters or farther out from the surface of that world. Calhoun's
little ship should repair to that spot. The giant landing grid should
then reach out its specialized force-field and lock onto the ship, and
then bring it gently but irresistibly down to ground. Then Calhoun,
representing Med Service, should confer gravely with planetary
authorities about public health conditions on Maris III.

It was not to be expected that anything important would turn up.
Calhoun would deliver full details of recent advances in the progress
of medicine. These might already have reached Maris III in the ordinary
course of commerce, but he would make sure. He might--but it was
unlikely--learn of some novelty worked out here. In any case, within
three days he should return to the small Med Ship, the landing grid
should heave it firmly heavenward to not less than five planetary
diameters distance, and there release it. And Calhoun and Murgatroyd
and the Med Ship should flick into overdrive and speed back toward
Headquarters, from whence they had come.

       *       *       *       *       *

Right now, Calhoun waited for an answer to his landing call. But he
regarded the vast disk of the nearby planet.

"By the map," he observed to Murgatroyd, "the city ought to be on the
shore of that bay somewhere near the terminus. Close to the sunset
line."

His call was answered. A voice said incredulously on the space-phone
speaker:

"_What? What's that? What's that you say?_"

"Med Ship _Aesclipus Twenty_," Calhoun repeated patiently. "Requesting
co-ordinates for landing. Our mass is fifty tons. Repeat, five-oh tons.
Purpose of landing, planetary health inspection."

The voice said more incredulously still:

"_A Med Ship? Holy_--" By the change of sound, the man down on the
planet had turned away from the microphone. "_Hey! Listen to this_--"

There was abrupt silence. Calhoun raised his eyebrows. He drummed on
the control desk before him.

There was a long pause. A very long pause. Then a new voice came on
the space phone, up from the ground:

"_You up aloft there! Identify yourself!_"

Calhoun said very politely:

"This is Med Ship _Aesclipus Twenty_. I would like to come to ground.
Purpose of landing, health inspection."

"_Wait_," said the voice from the planet. It sounded strained.

A murmuring sounded, transmitted from fifty thousand miles away. Then
there was a click. The transmitter down below had cut off. Calhoun
raised his eyebrows again. This was not according to routine. Not
at all! The Med Service was badly overworked and understaffed. The
resources of interplanetary services were always apt to be stretched to
their utmost, because there could be no galactic government as such.
Some thousands of occupied planets, the closest of them light-years
apart--or weeks of traveling--couldn't hold elections or have political
parties for the simple reason that travel even in overdrive was too
slow. They could only have service organizations whose authority
depended on the consent of the people served, and whose support had to
be gathered when and as it was possible.

But the Med Service was admittedly important. The local Sector
Headquarters was in the Cetis cluster. It was a sort of interstellar
clinic, with additions. It gathered and disseminated the results
of experience in health and medicine among some thousands of
colony-worlds, and from time to time it made contact with other
Headquarters carrying on the same work elsewhere. It admittedly
took fifty years for a new technique in gene-selection to cross the
so-far-occupied part of the galaxy, but it was a three-year voyage
in overdrive to cover the same distance direct. And the Med Service
was worth while. There was no problem of human ecological adjustment
it had so far been unable to solve, and there were some dozens of
planets whose human colonies owed their existence to it. There was
nowhere--nowhere at all--that a Med Ship was not welcomed on its errand
from Headquarters.

"Aground there!" said Calhoun sharply. "What's the matter? Are you
landing me or not?"

There was no answer. Then, suddenly, every sound-producing device in
the ship abruptly emitted a hoarse and monstrous noise. The lights
flashed up and circuit-breakers cut them off. The nearby-object horn
squawked. The hull-temperature warning squealed. The ship's internal
gravity-field tugged horribly for an instant and went off. Every device
within the ship designed to notify emergency clanged or shrieked or
roared or screamed. There was a momentary bedlam.

It lasted for part of a second only. Then everything stopped. There was
no weight within the ship, and there were no lights, and there was dead
silence, and Murgatroyd made whimpering sounds in the darkness.

Calhoun thought absurdly to himself, "_According to the book, this is
an unfavorable chance consequence of something or other._" But it was
more than an unfavorable chance occurrence. It was an intentional and
drastic and possibly a deadly one.

"Somebody's acting up," said Calhoun measuredly, in the blackness.
"What's the matter with them?"

He flipped the screen switch to bring back vision of what was outside.
The vision screens of a ship are very carefully fused against over-load
burnouts, because there is nothing in all the cosmos quite as helpless
and foredoomed as a ship which is blind in the emptiness of space. But
the screens did not light again. They couldn't. The cutouts hadn't
worked in time.

Calhoun's scalp crawled. But as his eyes adjusted, he saw the palely
fluorescent handles of switches and doors. They hadn't been made
fluorescent in expectation of an emergency like this, of course, but
they would help a great deal. He knew what had happened. It couldn't be
but one thing--a landing-grid field clamped on the fifty-ton Med Ship
with the power needed to grasp and land a twenty-thousand-ton liner.
At that strength it would paralyze every instrument and blow every
cut-off. It could not be accident. The reception of the news of his
identity, the repeated request that he identify himself, and then the
demand that he wait--This murderous performance was deliberate.

"Maybe," said Calhoun in the inky-black cabin, "as a Med Ship our
arrival is an unfavorable chance consequence of something--or the
unfavorableness is--and somebody means to keep us from happening. It
looks like it."

Murgatroyd whimpered.

"And I think," added Calhoun coldly, "that somebody may need a swift
kick in the negative feedback!"

He released himself from the safety belt and dived across the cabin
in which there was now no weight at all. In the blackness he opened a
cabinet door. What he did inside was customarily done by a man wearing
thick insulating gloves, in the landing grid back at Headquarters.
He threw certain switches which would allow the discharge of the
power-storage cells which worked the Med Ship's overdrive. Monstrous
quantities of energy were required to put even a fifty-ton ship
into overdrive, and monstrous amounts were returned when it came
out. The power amounted to ounces of pure, raw energy, and as a
safety-precaution such amounts were normally put into the Duhanne cells
only just before a Med Ship's launching, and drained out again on its
return. But now, Calhoun threw switches which made a rather incredible
amount of power available for dumping into the landing-grid field about
him--if necessary.

He floated back to the control chair.

       *       *       *       *       *

The ship lurched--violently. It was being moved by the grid field
without any gentleness at all. Calhoun's hands barely grasped the back
of his pilot's chair before the jerk came, and it almost tore them
free. He just missed being flung against the back wall of the cabin by
the applied acceleration. But he was a long way out from the planet. He
was at the end of a lever fifty thousand miles long. For that lever to
be used to shake him too brutally would require special adjustments.
But somebody was making them. The jerk reversed directions. He was
flung savagely against the chair to which he'd been clinging. He
struggled. Another yank, in another direction. Another one still. It
flung him violently into the chair.

Behind him, Murgatroyd squealed angrily as he went hurtling across the
cabin. He grabbed for holding-places with all four paws and his tail.

Another shake. Calhoun had barely clipped the safety belt fast before
a furious jolt nearly flung him out of it again to crash against the
cabin ceiling. Yet another vicious surge of acceleration. He scrabbled
for the controls. The yanks and plungings of the ship increased
intolerably. He was nauseated. Once he was thrust so furiously into the
control chair that he was on the verge of blacking out, and then the
direction of thrust was changed to the exact opposite so that the blood
rushing to his head seemed about to explode it. His arms flailed out of
control. He became dazed. But when his hands were flung against the
control board, despite their bruising he tried to cling to the control
knobs, and each time he threw them over. Practically all his circuits
were blown, but there was one--

His numbing fingers threw it. There was a roar, so fierce that it
seemed an explosion. He'd reached the switch which made effective the
discharge-circuit of his Duhanne cells. He'd thrown it. It was designed
to let the little ship's overdrive power-reserve flow into storage
at Headquarters on return from duty. Now, though, it poured into the
landing-grid field outside. It amounted to hundreds of millions of
kilowatt hours, delivered in the fraction of a second. There was the
smell of ozone. The sound was like a thunder clap.

But abruptly there was a strange and incredible peace. The lights came
on waveringly as his shaking fingers restored the circuit-breakers.
Murgatroyd shrilled indignantly, clinging desperately to an instrument
rack. But the vision screens did not light again. Calhoun swore.
Swiftly, he threw more circuit-restorers. The nearest-object indicator
told of the presence of Maris III at forty-odd thousand miles.
The hull-temperature indicator was up some fifty-six degrees. The
internal-gravity field came on, faintly, and then built up to normal.
But the screens would not light. They were permanently dead. Calhoun
raged for seconds. Then he got hold of himself.

"_Chee-chee-chee!_" chattered Murgatroyd desperately. "_Chee-chee!_"

"Shut up!" growled Calhoun. "Some bright lad aground thought up a new
way to commit murder. Damned near got away with it, too! He figured
he'd shake us to death like a dog does a rat, only he was using a
landing-grid field to do it with! Right now, I hope I fried him!"

But it was not likely. Such quantities of power as are used to handle
twenty-thousand-ton space liners are not controlled direct, but
by relays. The power Calhoun had flung into the grid field should
have blown out the grid's transformers with a spectacular display
of fireworks, but it was hardly probable it had gotten back to the
individual at the controls.

"But I suspect," observed Calhoun vengefully, "that he'll consider this
business an unfavorable occurrence! Somebody'll twist his tail, too,
either for trying what he did or for not getting away with it! Only, as
a matter of pure precaution--"

His expression changed suddenly. He'd been trying not to think of the
consequences of having no sight of the cosmos outside the ship. Now he
remembered the electron telescope. It had not been in circuit, so it
could not have been burned out like his vision screens. He switched it
on. A star field appeared over his head.

"_Chee-chee!_" cried Murgatroyd hysterically.

Calhoun glanced at him. The jerking of the ship had shifted the
instruments in the rack to which Murgatroyd clung. Clipped into place
though they were, they'd caught Murgatroyd's tail and pinched it
tightly.

"You'll have to wait," snapped Calhoun. "Right now I've got to make us
look like a successful accident. Otherwise whoever tried to spread us
all over the cabin walls will try something else!"

The Med Ship flung through space in whatever direction and at
whatever velocity it had possessed when the grid field blew. Calhoun
shifted the electron-telescope field and simultaneously threw on the
emergency-rocket controls. There was a growling of the pencil-thin,
high-velocity blasts. There was a surging of the ship.

"No straight-line stuff," Calhoun reminded himself.

He swung the ship into a dizzy spiral, as if innumerable things had
been torn or battered loose in the ship and its rockets had come on of
themselves. Painstakingly, he jettisoned in one explosive burst all
the stored waste of his journey which could not be disposed of while
in overdrive. To any space-scanning instrument on the ground, it would
look like something detonating violently inside the ship.

"Now--"

The planet Maris III swung across the electron telescope's field. It
looked hideously near--but that was the telescope's magnification. Yet
Calhoun sweated. He looked at the nearest-object dial for reassurance.
The planet was nearer by a thousand miles.

"Hah!" said Calhoun.

He changed the ship's spiral course. He changed it again. He abruptly
reversed the direction of its turn. Adequate training in space-combat
might have helped plot an evasion-course, but it might have been
recognizable. Nobody could anticipate his maneuvers now, though. He
adjusted the telescope next time the planet swept across its field, and
flipped on the photorecorder. Then he pulled out of the spiral, whirled
the ship until the city was covered by the telescope, and ran the
recorder as long as he dared keep a straight course. Then he swooped
toward the planet in a crazy, twisting fall with erratic intermissions,
and made a final lunatic dash almost parallel to the planet's surface.

At five hundred miles, he unshielded the ports which of necessity had
to be kept covered in clear space. There was a sky which was vividly
bright with stars. There was a vast blackness off to starboard which
was the night side of the planet.

He went down. At four hundred miles the outside pressure indicator
wavered away from its pin. He used it like a pitot-tube recording,
doing sums in his head to figure the static pressure that should exist
at this height, to compare with the dynamic pressure produced by his
velocity through the near hard vacuum. The pressure should have been
substantially zero. He swung the ship end-for-end and killed velocity
to bring the pressure-indication down. The ship descended. Two hundred
miles. He saw the thin bright line of sunshine at the limb of the
planet. Down to one hundred. He cut the rockets and let the ship fall
silently, swinging it nose up.

       *       *       *       *       *

At ten miles he listened for man-made radiation. There was nothing in
the electromagnetic spectrum but the crackling of static in an electric
storm which might be a thousand miles away. At five miles height the
nearest-object indicator, near the bottom of its scale, wavered in a
fashion to prove that he was still moving laterally across mountainous
country. He swung the ship and killed that velocity, too.

At two miles he used the rockets for deceleration. The pencil-thin
flame reached down for an incredible distance. By naked-eye observation
out a port he tilted the fiercely-roaring, swiftly-falling ship until
hillsides and forests underneath him ceased to move. By that time he
was very low indeed.

He reached ground on a mountainside which was lighted by the blue-white
flame of the rocket-blast. He chose an area in which the tree tops were
almost flat, indicating something like a plateau underneath. Murgatroyd
was practically frantic by this time because of his capture and the
pinching of his tail, but Calhoun could not spare time to release
him. He let the ship down gently, gently, trying to descend in an
absolutely vertical line.

If he didn't do it perfectly, he came very close. The ship settled
into what was practically a burned-away tunnel among monstrous trees.
The high-velocity slender flame did not splash when it reached ground.
It penetrated. It burned a hole for itself through humus and clay
and bedrock. When the ship touched and settled, there was boiling
molten stone some sixty feet underground, but there was a small
scratching sound as it came to rest. A flame-amputated tree-limb rubbed
tentatively against the hull.

Calhoun turned off the rockets. The ship swayed slightly and there were
crunching noises. Then it was still on its landing fins.

"Now," said Calhoun, "I can take care of you, Murgatroyd."

He flicked on the switches of the exterior microphones--much more
sensitive than human ears. The radiation-detectors were still in
action. They reported only the cracklings of the distant storm.

But the microphones brought in the moaning of wind over nearby
mountaintops, and the almost deafening susurrus of rustling leaves.
Underneath these noises there was a bedlam of other natural sounds.
There were chirpings and hootings and squeaks, and the gruntings made
by native animal life. These sounds had a singularly peaceful quality.
When Calhoun toned them down to be no more than background-noises, they
suggested the sort of concert of night-creatures which to men has
always seemed an indication of purest tranquility.

Presently Calhoun looked at the pictures the photorecorder had taken
while the telescope's field swept over the city. It was the colony-city
reported to have been begun two years before, to receive colonists from
Dettra Two. It was the city of the landing grid which had tried to
destroy the Med Ship as a dog kills a rat--by shaking it to fragments,
some fifty thousand miles in space. It was the city which had made
Calhoun land with his vision-plates blinded, that had made him pretend
his ship was internally a wreck: which had drained his power-reserves
of some hundreds of millions of kilowatt hours of energy. It was the
city which had made his return to Med Headquarters impossible.

He inspected the telescopic pictures. They were very clear. They showed
the city with astonishing detail. There was a lacy pattern of highways,
with their medallions of multiple-dwelling units. There were the lavish
park areas between the buildings of this planetary capital. There was
the landing grid itself--a half-mile-high structure of steel girders, a
full mile in diameter.

But there were no vehicles on the highways. There were no specks on the
crossing bridges to indicate people on foot. There were no copters on
the building roofs, nor were there objects in mid-air to tell of air
traffic.

The city was either deserted or it had never been occupied. But it was
absolutely intact. The structures were perfect. There was no indication
of past panic or disaster, and even the highways had not been overgrown
by vegetation. But it was empty--or else it was dead.

But somebody in it had tried very ferociously and with singular
effectiveness to try to destroy the Med Ship.

Because it was a Med Ship.

Calhoun raised his eyebrows and looked at Murgatroyd.

"Why is all this?" he asked. "Have you any ideas?"

"_Chee!_" shrilled Murgatroyd.




                                  II

    "The purpose of a contemplated human action is always the attainment
    of a desired subjective experience. But a subjective experience
    is desired both in terms of intensity, and in terms of duration.
    For an individual the temptingness of different degrees of
    intensity-of-experience is readily computed. However, the
    temptingness of different durations is equally necessary for the
    computation of the probability of a given individual performing
    a given action. This modification of desirability by expectable
    duration depends on the individual's time-sense: its acuity and its
    accuracy. Measurements of time-sense--"

                                        _Probability and Human Conduct_
                                                             Fitzgerald


Two days later Calhoun found a cultivated field and a dead man, but
before that he found only bewilderment. Before leaving the Med Ship, he
very carefully monitored all over again the entire radiation spectrum
for man-made signals. There were no communications in the air of Maris
III--which on the face of it was proof that the planet was uninhabited.
But the ship's external microphones picked up a rocket roar in
mid-morning of the day after Calhoun's landing. By the time the sound
reached the ground, of course, the rocket itself was far below the
horizon; but Calhoun saw the faint white trail of its passage against
the blue of the sky. The fact that he saw it, in daytime, was proof
that it was within the atmosphere. Which, in turn, said that the rocket
was taking photographs from high altitude for signs of the crater the
Med Ship should have made in an uncontrolled landing.

The fact of search proved that the planet was inhabited, and the
silence of the radio spectrum said that it wasn't. The absence of
traffic in the city said that it was dead or empty, but there were
people there because they'd answered Calhoun's hail, and tried to kill
him when he identified himself. But nobody would want to destroy a Med
Ship except to prevent a health inspection, and nobody would want to
prevent an inspection unless there was a situation aground that the Med
Service ought to know about. But there should not possibly be such a
situation.

There was no logical explanation for such a series of contradictions.
Civilized men acted this way or that. There could only be civilized men
here. They acted neither this way nor that. Therefore--the confusion
began all over again.

Calhoun dictated an account of events to date into the emergency
responder in the ship. If a search-call came from space, the responder
would broadcast this data and Calhoun's intended action. He carefully
shut off all other operating circuits so the ship couldn't be found by
their radiation. He equipped himself for travel, and he and Murgatroyd
left the ship. Obviously, he headed toward the city where whatever was
wrong was centered.

Travel on foot was unaccustomed, but not difficult. The vegetation
was semi-familiar. Maris III was an Earth-type planet and circled a
Sol-type sun, and given similar conditions of gravity, air, sunlight,
and temperature-range, similar organisms should develop. There would
be room, for example, for low-growing ground-cover plants and there
would also be advantages to height. There would be some equivalent of
grasses, and there would be the equivalent of trees, with intermediate
forms having in-between habits of growth. Similar reasoning would apply
to animal life. There would be parallel ecological niches for animals
to fill, and animals would adapt to fill them.

Maris III was not, then, an "unearthly" environment. It was much
more like an unfamiliar part of a known planet than a new world
altogether. But there were some oddities. An herbivorous creature
without legs which squirmed like a snake. It lived in holes. A
pigeon-sized creature whose wings were modified, gossamer-thin scales
with iridescent colorings. There were creatures which seemed to live
in lunatic association, and Calhoun was irritably curious to know if
they were really symbiotes or only unrecognizable forms of the same
organism, like the terrestrial male and female firefly-glowworm.

But he was heading for the city. He couldn't spare time to biologize.
On his first day's journey he looked for food to save the rations he
carried. Murgatroyd was handy, here. The little _tormal_ had his place
in human society. He was friendly, and he was passionately imitative
of human beings, and he had a definite psychology of his own. But he
was useful, too. When Calhoun strode through the forests which had
such curiously un-leaflike foliage, Murgatroyd strode grandly with
him, imitating his walk. From time to time he dropped to all four paws
to investigate something. He invariably caught up with Calhoun within
seconds.

Once Calhoun saw him interestedly bite a tiny bit out of a most
unpromising looking shrub-stalk. He savored its flavor, and then
swallowed it. Calhoun took note of the plant and cut off a section. He
bound it to the skin of his arm up near the elbow. Hours later there
was no allergic reaction, so he tasted it. It was almost familiar.
It had the flavor of a bracken-shoot, mingled with a fruity taste.
It would be a green bulk-food like spinach or asparagus, filling but
without much substance.

Later, Murgatroyd carefully examined a luscious-seeming fruit which
grew low enough for him to pluck. He sniffed it closely and drew
back. Calhoun noted that plant, too. Murgatroyd's tribe was bred
at Headquarters for some highly valuable qualities. One was a very
sensitive stomach--but it was only one. Murgatroyd's metabolism was
very close to man's. If he ate something and it didn't disagree with
him, it was very likely safe for a man to eat it, too. If he rejected
something, it probably wasn't. But his real value was much more
important than the tasting of questionable foods.

When Calhoun camped the first night, he made a fire of a plant shaped
like a cactus-barrel and permeated with oil. By heaping dirt around it,
he confined its burning to a round space very much like the direct-heat
element of an electronic stove. It was an odd illustration of the fact
that human progress does not involve anything really new in kind,
but only increased convenience and availability of highly primitive
comforts. By the light of that circular bonfire, Calhoun actually read
a little. But the light was inadequate. Presently he yawned. One did
not get very far in the Med Service without knowing probability in
human conduct. It enabled one to check on the accuracy of statements
made, whether by patients or officials, to a Med Ship man. Today,
though, he'd traveled a long way on foot. He glanced at Murgatroyd, who
was gravely pretending to read from a singularly straight-edged leaf.

"Murgatroyd," said Calhoun, "it is likely that you will interpret any
strange sound as a possible undesirable subjective experience. Which
is to say, as dangerous. So if you hear anything sizable coming close
during the night, I hope you'll squeal. Thank you."

Murgatroyd said "_Chee_," and Calhoun rolled over and went to sleep.

       *       *       *       *       *

It was mid-morning of the next day when he came upon a cultivated
field. It had been cleared and planted, of course, in preparation
for the colonists who'd been expected to occupy the city. Familiar
Earth-plants grew in it, ten feet high and more. And Calhoun examined
it carefully, in the hope of finding how long since it had received
attention. In his examination, he found the dead man.

As a corpse, the man was brand-new, and Calhoun very carefully put
himself into a strictly medical frame of mind before he bent over for
a technical estimate of what had happened, and when. The dead man
seemed to have died of hunger. He was terribly emaciated, and he didn't
belong in a cultivated field far from the city. By his garments he was
a city-dweller and a prosperous one. He wore the jewels which nowadays
indicated a man's profession and status in it much more than the
value of his possessions. There was money in his pockets, and writing
materials, a wallet with pictures and identification, and the normal
oddments a man would carry. He'd been a civil servant. And he shouldn't
have died of starvation.

He especially shouldn't have gone hungry here! The sweet-maize plants
were tall and green. Their ears were ripe. He hadn't gone hungry! There
were the inedible remains of at least two dozen sweet-maize ears.
They had been eaten some time--some days--ago, and one had been left
unfinished. If the dead man had eaten them but was unable to digest
them, his belly should have been swollen with undigested food. It
wasn't. He'd eaten and digested and still had died, at least largely of
inanition.

Calhoun scowled.

"How about this corn, Murgatroyd?" he demanded.

He reached up and broke off a half-yard-long ear. He stripped away
the protecting, stringy leaves. The soft grains underneath looked
appetizing. They smelled like good fresh food. Calhoun offered the ear
to Murgatroyd.

The little _tormal_ took it in his paws and on the instant was eating
it with gusto.

"If you keep it down, he didn't die of eating it," said Calhoun,
frowning, "and if he ate it--which he did--he didn't die of starvation.
Which he did."

He waited. Murgatroyd consumed every grain upon the oversized cob. His
furry belly distended a little. Calhoun offered him a second ear. He
set to work on that, too, with self-evident enjoyment.

"In all history," said Calhoun, "nobody's ever been able to
poison one of you _tormals_ because your digestive system has a
qualitative-analysis unit in it that yells bloody murder if anything's
likely to disagree with you. As a probability of _tormal_ reaction,
you'd have been nauseated before now if that stuff wasn't good to eat."

But Murgatroyd ate until he was distinctly pot-bellied. He left a few
grains on the second ear with obvious regret. He put it down carefully
on the ground. He shifted his left-hand whiskers with his paw and
elaborately licked them clean. He did the same to the whiskers on the
right-hand side of his mouth. He said comfortably:

"_Chee!_"

"Then that's that," Calhoun told him. "This man didn't die of
starvation. I'm getting queasy!"

He had his lab kit in his shoulder-pack, of course. It was an
absurdly small outfit, with almost microscopic instruments. But in
Med Ship field work the techniques of microanalysis were standard.
Distastefully, Calhoun took the tiny tissue-sample from which he could
gather necessary information. Standing, he ran through the analytic
process that seemed called for. When he finished, he buried the dead
man as well as he could and started off in the direction of the city
again. He scowled as he walked.

He journeyed for nearly half an hour before he spoke. Murgatroyd
accompanied him on all fours, now, because of his heavy meal. After a
mile and a half, Calhoun stopped and said grimly:

"Let's check you over, Murgatroyd."

He verified the _tormal's_ pulse and respiration and temperature. He
put a tiny breath-sample through the part of the lab kit which read off
a basic metabolism rate. The small animal was quite accustomed to the
process. He submitted blandly. The result of the checkover was that
Murgatroyd the _tormal_ was perfectly normal.

"But," said Calhoun angrily, "that man died of starvation! There was
practically no fat in that tissue-sample at all! He arrived where
we found him while he was strong enough to eat, and he stayed where
there was good food, and he ate it, and he digested it, and he died of
starvation! Why?"

Murgatroyd wriggled unhappily, because Calhoun's tone was accusing. He
said, "_Chee!_" in a subdued tone of voice. He looked pleadingly up at
Calhoun.

"I'm not angry with you," Calhoun told him, "but dammit--"

He packed the lab kit back into his pack, which contained food for the
two of them for about a week.

"Come along!" he said bitterly. He started off. Ten minutes later he
stopped. "What I said was impossible. But it happened, so it mustn't
have been what I said. I must have stated it wrongly. He could eat,
because he did. He did eat, because of the cobs left. He did digest it.
So why did he die of starvation? Did he stop eating?"

"_Chee!_" said Murgatroyd, with conviction.

       *       *       *       *       *

Calhoun grunted and marched on once more. The man had not died of a
disease--not directly. The tissue analysis gave a picture of death
which denied that it came of any organ ceasing to function. Was it
the failure of the organism--the man--to take the action required for
living? Had he stopped eating?

Calhoun's mind skirted the notion warily. It was not plausible. The man
had been able to feed himself and had done so. Anything which came upon
him and made him unable to feed himself--

"He was a city man," growled Calhoun. "And this is a long way from the
city. What was he doing away out here, anyhow?"

He hesitated and tramped on again. A city man found starved in a remote
place might have become lost, somehow. But if this man was lost, he was
assuredly not without food.

"If there was a ground-car," Calhoun considered, "it wouldn't mean
anything. If he dared go back to the city he might have used it, but he
wouldn't have been where I found him if he hadn't wanted or needed to
leave the city. Hm-m-m--He walked out into the middle of the field. He
was hungry--why didn't he have food?--and he ate. He stayed there for
days, judging by the amount of food he ate _and_ digested. Why did he
do that? Then he stopped eating and died. Again why?"

He crossed over the top of a rounded hillock some three miles from the
shallow grave he'd made. He began to accept the idea that the dead man
had stopped eating, for some reason, as the only possible explanation.
But that didn't make it plausible. He saw another ridge of higher hills
ahead.

In another hour he came to the crest of that farther range. It was the
worn-down remnant of a very ancient mountain-range, now eroded to a
mere fifteen hundred or two thousand feet. He stopped at the very top.
Here was a time and place to look and take note of what he saw. The
ground stretched away in gently rolling fashion for very many miles,
and there was the blue blink of sea at the horizon. A little to the
left he saw shining white. He grunted.

That was the city of Maris III, which had been built to receive
colonists from Dettra and relieve the population-pressure there. It
had been planned as the nucleus of a splendid, spacious, civilized
world-nation to be added to the number of human-occupied worlds. From
its beginning it should hold a population in the hundreds of thousands.
It was surrounded by cultivated fields, and the air above it should be
a-shimmer with flying things belonging to its inhabitants.

Calhoun stared at it through his binoculars. They could not make an
image, even so near, to compare to that the electron telescope had
made from space, but he could see much. The city was perfect. It was
intact. It was new. But there was no sign of occupancy anywhere in it.
It did not look dead, so much as frozen. There were no fliers above it.
There was no motion on the highways. He saw one straight road which
ran directly away along his line of sight. Had there been vehicles on
it, he would have seen at least shifting patches of color as clots of
traffic moved together. There were none.

He pressed his lips together. He began to inspect the nearer terrain.
He saw foreshortened areas where square miles of ground had been
cleared and planted to Earth vegetation. The ground would have been
bulldozed clean, and then great sterilizers would have lumbered back
and forth, killing every native seed and root and even the native
soil-bacteria. Then there would have been spraying with cultures of
the nitrogen-fixing and phosphorous-releasing microscopic organisms
which normally lived in symbiosis with Earth-plants. They would have
been tested beforehand for their ability to compete with indigenous
bacterial life. And then Earth-plants would have been seeded.

They had been. Calhoun saw that inimitable green which a man somehow
always recognizes. It is the green of plants whose ancestors throve on
Earth and have followed that old planet's children halfway across the
galaxy.

"The population must be practically nothing," growled Calhoun,
"because it doesn't show. But the part of it in the city wants to keep
whatever's happened from the Med Service. Hm-m-m. They're not dying, or
they'd want help. But at least one dead man wasn't in the city where he
belonged, and he could have used some help! Maybe there are more like
him."

Murgatroyd said,

"_Chee!_"

"If there are two kinds of people here," added Calhoun darkly, "they
might be--antagonistic to each other."

He stared with knitted brows over the vast expanse toward the horizon.
Murgatroyd had halted a little behind him. He stood up on his hind legs
and stared intently off to one side. He shaded his eyes with a forepaw
in a singularly humanlike fashion and looked inquisitively at something
he saw. But Calhoun did not notice.

"Make a guess, Murgatroyd," said Calhoun. "There are at least a few
people in the city who don't want something known to the Med Service.
So whatever's the matter, it's not fatal to them. There may be people
wandering about like that poor devil we found. Something was fatal to
him! Where'd we find more of his type? Since they haven't tried to
kill me, we might make friends."

Murgatroyd did not answer. He stared absorbedly at a patch of
underbrush some fifty yards to the left.

       *       *       *       *       *

Calhoun shrugged and started down the hillside. Murgatroyd remained
fixed in a pose of intensely curious attention to the patch of brush.
Calhoun went on down the farther hillside. His back was toward the
brush-thicket.

There was a deep-toned, musical twanging sound from the thicket.
Calhoun's body jerked violently as an impact sounded. He stumbled and
went down, with the shaft of a wooden projectile sticking out of his
pack. He lay still.

Murgatroyd whimpered. He rushed to where Calhoun lay upon the ground.
He danced in agitation, chattering shrilly. He wrung his paws in
humanlike distress. He whimpered and chattered together. He tugged at
Calhoun. Calhoun made no response.

A figure came out of the thicket. It was gaunt and thin, yet its
garments had once been of admirable quality. It carried a strange and
utterly primitive weapon. It moved toward Calhoun without lightness,
but with a dreary resolution.

It bent over him and laid a hand to the wooden projectile it had fired
into his back.

Calhoun moved suddenly. He grappled. The gaunt figure toppled, and he
swarmed upon it savagely as it struggled. But it was taken by surprise.
Pantings sounded, and Murgatroyd danced in a fever of anxiety.

Then Calhoun stood up quickly. He stared down at the emaciated figure
which had tried to murder him from ambush. That figure panted horribly,
now.

"Really," said Calhoun in a professional tone, "as a doctor I'd say
that you should be in bed instead of wandering around trying to murder
total strangers. When did this trouble begin? I'm going to take your
temperature and your pulse. Murgatroyd and I have been hoping to find
someone like you. The only other human being I've seen on this planet
wasn't able to talk."

He swung his shoulder-pack around and impatiently jerked a
sharp-pointed stick out of it. It was the missile, which had been
stopped by the pack. He brought out his lab kit. With absolute
absorption in the task, he prepared to make a swift check of his
would-be murderer's state of health.

It was not good. There was already marked emaciation. The desperately
panting young woman's eyes were deep-sunk: hollow. She gasped and
gasped. Still gasping, she lapsed into unconsciousness.

"Here," said Calhoun curtly, "you enter the picture, Murgatroyd! This
is the sort of thing you're designed to handle!"

He set to work briskly. But presently he said over his shoulder:

"Besides a delicate digestion and a hair-trigger antibody system,
Murgatroyd, you ought to have the instincts of a watchdog. I don't
like coming that close to being speared by my patients. See if there's
anybody else around, won't you?"

"_Chee!_" said Murgatroyd shrilly. But he didn't understand. He watched
as Calhoun deftly drew a small sample of blood from the unconscious
young woman and painstakingly put half the tiny quantity into an almost
microscopic ampule in the lab kit. Then he moved toward Murgatroyd.

The _tormal_ wriggled as Calhoun made the injection. But it did not
hurt. There was an insensitive spot on his flank where the pain-nerves
had been blocked off before he was a week old.

"As one medical man to another," said Calhoun, "what's a good treatment
for anoxia when you haven't got any oxygen? You don't know? Neither do
I. But we've found out why those chaps in the city tried to shake us to
bits, out in space."

He swore in a sudden, bitter anger. Then he looked quickly at the girl,
concerned lest she'd heard.

She hadn't. She was still unconscious.




                                  III

    "That pattern of human conduct which is loosely called
    "self-respecting" has the curious property of restricting to
    the individual--through his withdrawal of acts to communicate
    misfortune--the unfavorable chance occurrences which probability
    insists must take place. On the other hand, the same pattern of
    human conduct tends to disseminate and to share chance favorable
    occurrences among the group. The members of a group of persons
    practicing "self-respect," then, increase the mathematical
    probability of good fortune to all their number. This explains
    the instability of cultures in which principles leading to this
    type of behavior become obsolete. A decadent society brings bad
    luck upon itself by the operation of the laws of probability...."

                                        _Probability and Human Conduct_
                                                             Fitzgerald


She came very slowly back to consciousness. It was almost as if she
waked from utterly exhausted sleep. When she first opened her eyes,
they wandered vaguely until they fell upon Calhoun. Then a bitter and
contemptuous hatred filled them. Her hand fumbled weakly to the knife
at her waist. It was not a good weapon. It had been table-cutlery and
the handle was much too slender to permit a grip by which somebody
could be killed. Calhoun bent over and took the knife away from her. It
had been ground unskillfully to a point.

"In my capacity as your doctor," he told her, "I must forbid you to
stab me. It wouldn't be good for you." Then he said, "Look! My name's
Calhoun. I came from Sector Med Headquarters to make a planetary health
inspection, and some lads in the city apparently didn't want a Med Ship
aground. So they tried to kill me by buttering me all over the walls
of my ship, with the landing-grid field. I made what was practically a
crash landing, and now I need to know what's up."

The burning hatred remained in her eyes, but there was a trace of
doubt.

"Here," said Calhoun, "is my identification."

He showed her the highly official documents which gave him vast
authority--where a planetary government was willing to concede it.

"Of course," he added, "papers can be stolen. But I have a witness that
I'm what and who I say I am. You've heard of _tormals_? Murgatroyd will
vouch for me."

He called his small and furry companion. Murgatroyd advanced and
politely offered a small, prehensile paw. He said "_Chee_" in his
shrill voice, and then solemnly took hold of the girl's wrist in
imitation of Calhoun's previous action of feeling her pulse.

Calhoun watched. The girl stared at Murgatroyd. But all the galaxy had
heard of _tormals_. They'd been found on a planet in the Deneb region,
and they were engaging pets and displayed an extraordinary immunity to
the diseases men were apt to scatter in their interstellar journeyings.
A forgotten Med Service researcher made an investigation on the ability
of _tormals_ to live in contact with men. He came up with a discovery
which made them very much too valuable to have their lives wasted in
mere sociability. There were still not enough of Murgatroyd's kind to
meet the need that men had of them, and laymen had to forego their
distinctly charming society. So Murgatroyd was an identification.

The girl said faintly:

"If you'd only come earlier.... But it's too late now! I ... thought
you came from the city."

"I was headed there," said Calhoun.

"They'll kill you--"

"Yes," agreed Calhoun, "they probably will. But right now you're ill
and I'm Med Service. I suspect there's been an epidemic of some disease
here, and that for some reason the people in the city don't want the
Med Service to know about it. You seem to have ... whatever it is. Also
you had a very curious weapon to shoot me with."

The girl said drearily:

"One of our group had made a hobby of such things. Ancient weapons.
He had bows and arrows and--what I shot you with was a crossbow. It
doesn't need power. Not even chemical explosives. So, when we ran away
from the city, he ventured back in and armed us as well as he could."

       *       *       *       *       *

Calhoun nodded. A little irrelevant talk is always useful at the
beginning of a patient-interview. But what she said was not irrelevant.
A group of people had fled the city. They'd needed arms, and one of
their number had "ventured" back into the city for them. He'd known
where to find only reconstructions of ancient lethal devices--a hobby
collection. It sounded like people of the civil-service type. Of course
there were no longer social classes separated by income. Not on most
worlds, anyhow. But there were social groupings based on similar
tastes, which had led to similar occupations and went on to natural
congeniality. Calhoun placed her, now. He remembered a long-out-moded
term, "upper middle class" which no longer meant anything in economics
but did in medicine.

"I'd like a case-history," he said conversationally. "Name?"

"Helen Jons," she said wearily.

He held the mike of his pocket recorder to pick up her answers.
Occupation, statistician. She'd been a member of the office force which
was needed during the building of the city. When the construction work
was finished, most of the workmen returned to the mother-world Dettra,
but the office staff stayed on to organize things when colonists should
arrive.

The plague appeared among the last shipload of workmen waiting to be
returned to the mother world. There were about a thousand persons
in the city altogether. The disease produced, at first, no obvious
physical symptoms, but those afflicted with it tended to be listless
and lackadaisical and without energy. The first-noticed symptom was
a cessation of gripes and quarrelings among the workmen. Shortness
of breath appeared two days later. It was progressive. Deaths
began in two weeks. Men sank into unconsciousness and died. By the
time the transport-ship arrived from Dettra with colonists to be
landed ... it was to take back the workmen ... the physicians on
the planet were grim. They described the situation by space phone.
The transport returned to Dettra without removing the workmen or
landing the colonists. The people left in the city on Maris III were
self-quarantined, but they expected help.

It was two months before another ship arrived. By then fewer than
two hundred of the original thousand remained. More than half those
survivors were already listless and short-breathed. A good ten per cent
were in the beginning of that marked lethargy which deepened into coma
and ended fatally. A desperate, gaunt, plague-stricken few still manned
the landing grid.

The ship came down. Men disembarked. There was no crowd to greet them.
The survivors still in the city had scattered themselves widely,
hoping to escape the contagion by isolating themselves in new and
uncontaminated dwelling-units. But there was no lack of communication
facilities. Nearly all the survivors watched on vision screens in
contact with the landing grid.

The newcomers did not look like doctors, nor act like them. Visiphone
contact with the landing grid was immediately broken. It could not be
restored. So the isolated groups spoke agitatedly to each other by
other visiphone contacts, exchanging messages of desperate hope. Then,
new-landed men appeared at an apartment whose occupant was in the act
of such a conversation with a group in a distant building. He left
the visiphone on as he went to admit and greet the men he hoped were
researchers, at least, come to find the cause of the plague and end it.

The viewer at the other visiphone plate gazed eagerly into his friend's
apartment. He saw a group of the newcomers admitted. He saw them
deliberately murder his friend and the survivors of his family.

Plague-stricken or merely terrified people--in pairs or trios widely
separated through the city--communicated in swift desperation. It was
possible that there had been a mistake--a blunder; an unauthorized
crime had been committed. But it was not a mistake. Unthinkable as such
an idea was, there developed evidence that the plague on Maris III was
to be ended as if it were an epizootic among animals. Those who had it
and those who had been exposed to it were to be killed to prevent its
spread among the newcomers.

A conviction of such horror could not be accepted without absolute
proof. But when night fell, the public power-supply of the city was cut
off--communications ended. The singular sunset hush of Maris III left
utter stillness everywhere--and there were screams which echoed among
the city's innumerable empty-eyed, unoccupied buildings.

The scant remainder of the plague-survivors fled in the night. They
fled singly, carrying the plague with them. Some carried members of
their families already stricken. Some helped already-doomed wives or
friends or husbands to the open country. Flight would not save their
lives. It would only prevent their murder. But somehow that seemed a
thing to be attempted.

       *       *       *       *       *

"This," said Calhoun, "is not a history of your own case. When did you
develop the disease ... whatever it may be?"

"Don't you know what it is?" asked Helen hopelessly.

"Not yet," admitted Calhoun. "I've very little information. I'm trying
to get more now."

What other information he had he'd gathered from a newly dead man in a
field some miles away. He did not mention that at this moment.

The girl went on, exhaustedly. The first symptom was listlessness, of
which the victim was unconscious. One could pull out of it with an
effort, but one wasn't aware that anything was wrong. The listlessness
progressed. One could realize it only by recognizing the more urgent,
more violent effort needed to pay attention, and the discovery of
weakness when one tried to act. One did not feel discomfort--not even
hunger or thirst. One had to summon increasing resolution even to
become aware of the need to do anything at all.

The symptoms were singularly like those of a man too long at too high
an altitude without oxygen. They were even more like those of a man
in a non-pressurized flier whose oxygen supply has been cut off. But
such a man would pass out without realizing that he was slipping into
unconsciousness. On Maris III the process was infinitely gradual. It
was a matter of two weeks or more.

"I'd been infected before we ran away," she said drearily. "I didn't
know it then. Now I know I've a few more days of being able to think
and act ... if I try hard enough. But it'll be less and less each day.
Then I'll stop being able to try."

Calhoun watched the tiny recorder roll its multiple-channel tape from
one spool to the other as she talked.

"You had energy enough to try to kill me," he observed.

He looked at the weapon. There was an arched steel spring placed
crosswise at the end of a barrel like a sporting blast-rifle. Now he
saw a handle and a ratchet by which the spring was brought to tension,
storing up power to throw the missile. He asked:

"Who wound up this crossbow?"

Helen hesitated.

"Kim ... Kim Walpole."

"You're not a solitary refugee now? There are others of your group
still alive?"

She hesitated again, and then said:

"Some of us came to realize that staying apart didn't matter. We ...
couldn't hope to live, anyhow. We ... already had the plague. Kim
is ... one of us. He's the strongest. He ... wound up the crossbow for
me. He ... had the weapons to begin with."

Calhoun asked seemingly casual questions. She told him of a group of
fugitives remaining together because all were already doomed. There
had been eleven of them. Two were dead, now. Three others were in
the last lethargy. It was impossible to feed them. They were dying.
The strongest was Kim Walpole, who'd ventured back into the city to
bring out weapons for the rest. He'd led them, and now was still the
strongest and--so the girl considered--the wisest of them all.

They were waiting to die. But the newcomers to the planet--the
invaders, they believed--were not content to let them wait. Groups and
single hunters came out of the city and searched for them.

"Probably," said the girl dispassionately, "to burn our bodies
against contagion. They ... kill us so they won't have to wait. And
it's just ... seemed so horrible that we ... felt we ought to defend
our right to die naturally by ... dying fighting. That's why I ... shot
at you. I shouldn't have, but--"

She stopped, helplessly. Calhoun nodded.

The fugitives now aided each other simply to avoid murder. They
gathered together exhaustedly at nightfall, and those who were
strongest did what they could for the others. By day, those who
could walk scattered to separate hiding places, so that if one were
discovered, the others might still escape the indignity of being
butchered. They had no stronger motive than that. They were merely
trying to die with dignity, instead of being killed as sick beasts.
Which bespoke a tradition and an attitude which Calhoun approved.
People like these would know something of the science of probability in
human conduct. Only they would call it ethics. But the strangers--the
invaders--the occupiers of the city were of another type. They probably
came from another world.

"I don't like this," said Calhoun coldly. "Just a moment."

He went over to Murgatroyd. Murgatroyd seemed to droop a little.
Calhoun checked his breathing and listened to his heart. Murgatroyd
submitted, saying only "_Chee_" when Calhoun put him down.

"I'm going to help you to your rendezvous," said Calhoun abruptly.
"Murgatroyd's got the plague now. I ... exposed him to it, and he's
reacting fast. And I want to see the others of your group before
nightfall."

The girl just managed to get to her feet. Even speaking had tired her,
but she gamely though wearily moved off at a slant to the hillside's
slope. Calhoun picked up the odd weapon and examined it thoughtfully.
He wound it up as it was obviously meant to be. He picked up the
missile it had fired, and put it in place. He went after the girl,
carrying it. Murgatroyd brought up the rear.

Within a quarter of a mile the girl stopped and clung swaying to the
trunk of a slender tree. It was plain that she had to rest, and
dreaded getting off her feet because of the desperate effort needed to
arise.

"I'm going to carry you," said Calhoun firmly. "You tell me the way."

He picked her up bodily and marched on. She was light. She was not a
large girl, but she should have weighed more. Calhoun still carried the
quaint ancient-type weapon without difficulty.

Murgatroyd followed as Calhoun went up a small inclination on the
greater hillside and down a very narrow ravine. Through brushwood he
pushed until he came to a small open space where shelters had been made
for a dozen or so human beings. They were utterly primitive--merely
roofs of leafy branches over frameworks of sticks. But of course they
were not intended for permanent use. They were meant only to protect
plague-stricken folk while they waited to die.

But there was disaster here. Calhoun saw it before the girl could.
There were beds of leaves underneath the shelters. There were three
bodies lying upon them. They would be those refugees in the terminal
coma which--since the girl had described it--accounted for the dead man
Calhoun had found, dead of starvation with food-plants all around him.
But now Calhoun saw something more. He swung the girl swiftly in his
arms so that she would not see. He put her gently down and said:

"Stay still. Don't move. Don't turn."

       *       *       *       *       *

He went to make sure. A moment later he raged. Because it was Calhoun's
profession to combat death and illness in all its forms. He took his
profession seriously. And there are defeats, of course, which a medical
man has to accept, though unwillingly. But nobody in the profession,
and least of all a Med Ship man, could fail to be roused to fury by the
sight of people who should have been his patients, lying utterly still
with their throats cut.

He covered them with branches. He went back to Helen.

"This place has been found by somebody from the city," he told her
harshly. "The men in coma have been murdered. I advise you not to look.
At a guess, whoever did it is now trying to track down the rest of you."

He went grimly to the small open glade, searching the ground for
footprints. There was ground-cover at most places, but at the edge
of the clearing he found one set of heavy footprints going away. He
put his own foot beside a print and rested his weight on it. His foot
made a lesser depression. The other print had been made by a man
weighing more than Calhoun. Therefore it was not one of the party of
plague-victims.

He found another set of such footprints, entering the glade from
another spot.

"One man only," he said icily. "He won't think he has to be on guard,
because a city's administrative personnel--such as were left behind
for the plague to hit--doesn't usually have weapons among their
possessions. And he's confident that all of you are weak enough not to
be dangerous to him."

Helen did not turn pale. She was pale before. She stared numbly at
Calhoun. He looked grimly at the sky.

"It'll be sunset within the hour," he said savagely. "If it's the
intention of the newcomers ... the invaders to burn the bodies of all
plague victims, he'll come back here to dispose of these three. He
didn't do it before lest the smoke warn the rest of you. But he knows
the shelters held more than three people. He'll be back!"

Murgatroyd said "_Chee!_" in a bewildered fashion. He was on all fours,
and he regarded his paws as if they did not belong to him. He panted.

Calhoun checked him over. Respiration way up. Heart-action like that
of the girl Helen. His temperature was not up, but down. Calhoun said
remorsefully:

"You and I, Murgatroyd, have a bad time of it in our profession. But
mine is the worse. You don't have to play dirty tricks on me, and I've
had to, on you!"

Murgatroyd said "_Chee!_" and whimpered. Calhoun laid him gently on a
bed of leaves which was not occupied by a murdered man.

"Lie still!" he commanded. "Exercise is bad for you!"

He walked away. Murgatroyd whined faintly, but lay still as if
exhausted.

"I'm going to move you," Calhoun told the girl, "so you won't be
sighted if that man from the city comes back. And I've got to keep out
of sight for a while or your friends will mistake me for him. I count
on you to vouch for me later. Basically, I'm making an ambush." Then he
explained irritably, "I daren't try to trail him because he might not
backtrack to return here!"

He lifted the girl and placed her where she could see the glade in its
entirety, but would not be visible. He settled down himself a little
distance away. He was acutely dissatisfied with the measures he was
forced to take. He could not follow the murderer and leave Helen and
Murgatroyd unprotected, even though the murderer might find another
victim because he was not trailed. In any case Murgatroyd's life, just
now, was more important than the life of any human being on Maris III.
On him depended everything.

But Calhoun was not pleased with himself.

       *       *       *       *       *

There was silence except for the normal noises of living wild things.
There were fluting sounds, which later Calhoun would be told, from
crawling creatures not too much unlike the land-turtles of Earth.
There were deep-bass hummings, which came from the throats of
miniature creatures which might roughly be described as birds. There
were chirpings which were the cries of what might be approximately
described as wild pigs--except that they weren't. But the sun Maris
sank low toward the nearer hill-crests, and behind them, and there came
a strange, expectant hush over all the landscape. At sundown on Maris
III there is a singular period when the creatures of the day are silent
and those of the night are not yet active. Nothing moved. Nothing
stirred. Even the improbable foliage was still.

It was into this stillness and this half-light that small and
intermittent rustling sounds entered. Presently there was a faint
murmur of speech. A tall, gaunt young man came out of the brushwood,
supporting a pathetically feeble old man, barely able to walk. Calhoun
made a gesture of warning as the girl Helen opened her lips to speak.
The slowly moving pair--the young man moving exhaustedly, the older man
staggering with weakness despite his help--came into the glade. The
younger helped the older to sit down. He stood panting.

A woman and a man came together, assisting each other. There was barely
light enough from the sun's afterglow to show their faces, emaciated
and white.

A fifth feeble figure came tottering out of another opening in the
brush. He was dark-bearded and broad, and he had been a powerful man.
But now the plague lay heavily upon him.

They greeted each other listlessly. They had not yet discovered those
of their number who had been murdered.

The gaunt young man summoned his strength and moved toward the shelter
where Calhoun had covered an unseemly sight with branches.

Murgatroyd whimpered.

There came another rustling sound. But this had nothing of feebleness
in it. Someone pushed branches forthrightly out of his way. He came
striding confidently into the small open space. He was well-fleshed,
and his color was excellent. Calhoun automatically judged him to be in
superlative good health, slightly over-fleshed, and of that physical
type which suffers very few psychosomatic troubles because it lives
strictly and enjoyably in the present.

Calhoun stood up. He stepped out into the fading light just as
the sturdy last-comer grinned at the group of plague-stricken
semi-skeletons.

"Back, eh?" he said amiably. "Saved me a lot of trouble. I'll make one
job of it."

With leisurely confidence he reached to the blaster at his hip.

"Drop it!" snapped Calhoun, from quartering behind him. "Drop it!"

The sturdy man whirled. He saw Calhoun with a crossbow raised to cover
him. There was light enough to show that it was not a blast-rifle--in
fact, that it was no weapon of any kind modern men would ordinarily
know. But much more significant to the sturdy man was the fact that
Calhoun wore a uniform and was in good health.

He snatched out his blast-pistol with professional alertness.

And Calhoun shot him with the crossbow. It happened that he shot him
dead.




                                  IV

    "Statistically, it must be recognized that no human action is
    without consequences to the man who acts. Again statistically, it
    must be recognized that the consequences of an action tend with
    strong probability to follow the general pattern of the action. A
    violent action, for example, has a strong probability of violent
    consequences, and since some at least of the consequences of an
    act must affect the person acting, a man who acts violently exposes
    himself to the probability that chance consequences which affect
    him, if unfavorable, will be violently so."

                                        _Probability and Human Conduct_
                                                             Fitzgerald


Murgatroyd had been inoculated with a blood-sample from the girl Helen
some three hours or less before sunset. But it was one of the more
valuable genetic qualities of the _tormal_ race that they reacted to
bacterial infection as a human being reacts to medication. Medicine on
the skin of a human being rarely has any systemic effect. Medication on
mucus membrane penetrates better. Ingested medication--medicine that
is swallowed--has greater effectiveness still. But substances injected
into tissues or the blood-stream have most effect of all. A centigram
of almost any drug administered by injection will have an effect
close to that of a gram taken orally. It acts at once and there is no
modification by gastric juices.

Murgatroyd had had half a cubic centimeter of the girl's blood injected
into the spot on his flank where he could feel no pain. It contained
the unknown cause of the plague on Maris III. Its effect as injected
was incomparably greater than the same infectious material smeared
on his skin or swallowed. In either such case, of course, it would
have had no effect at all, because _tormals_ were to all intents and
purposes immune to ordinary contagions. Just as they had a built-in
unit in their digestive tract to cause the instant rejection of
unwholesome food, their body-cells had a built-in ability to produce
antibodies immediately the toxin of a pathogenic organism came into
contact with them. So _tormals_ were effectively safe against any
disease transmitted by ordinary methods of infection. Yet if a culture
of pathogenic bacteria--say--were injected into their blood stream,
their whole body set to work to turn out antibodies because all
their body was attacked. And all at once. There was practically no
incubation-period.

Murgatroyd, who had been given the plague in mid-afternoon, was
reacting violently to its toxins by sunset. But two hours after
darkness fell he arose and said shrilly, "_Chee-chee-chee!_" He'd been
sunk in heavy slumber. When he woke, there was a small fire in the
glade, about which the exhausted, emaciated fugitives consulted with
Calhoun. Calhoun was saying bitterly:

"Those characters in the city are immune! They have to be! And they
know they're immune, or they wouldn't risk contagion by murdering you
or handling the bodies of plague-victims to burn them! So they have to
know all about the plague--and they knew it before they arrived! They
came because they knew! That's why I shot that man with the crossbow,
instead of taking a blaster to him. I meant to wound him so I could
make him answer questions, but it's not an accurate weapon and I killed
him instead. I got very little from the stuff in his pockets. The
only significant thing was a ground-car key, and even that means only
there's a car waiting somewhere for him."

The gaunt young man said drearily:

"He didn't come from Dettra, our home planet. Fashions are different on
different worlds. His foot-wear was like a style we had on Dettra four
years back, and his body-clothing has fasteners we don't use."

Murgatroyd saw Calhoun and rushed to him, embracing his legs with
enthusiasm and chattering shrilly of his relief at finding the man he
knew. The skeletonlike plague-victims stared at him.

"This," said Calhoun with infinite relief, "is Murgatroyd. He's had the
plague and is over it. So now we'll get you people cured. I wish I had
better light!"

He counted Murgatroyd's breathing and listened to his heart. Murgatroyd
was in that state of boisterous good health which is normal in any
lower animal, but amounts to genius in a _tormal_. Calhoun regarded him
with satisfaction.

"All right!" he said. "Come along!"

       *       *       *       *       *

He plucked a brand of burning resinous stuff from the campfire. He
handed it to the gaunt young man and led the way. Murgatroyd ambled
complacently after him. Calhoun stopped under one of the unoccupied
shelters and got out his lab kit. He bent over Murgatroyd. What he did,
did not hurt. When he stood up, he squinted at the red fluid in the
instrument he'd used.

"About fifteen CCs," he observed. "This is strictly emergency stuff I'm
doing now. But I'd say that there's an emergency."

The gaunt young man said:

"I'd say you've doomed yourself. The incubation-period seems to be
about six days. It took that long to develop among the doctors we had
in the office staff."

Calhoun opened a compartment of the kit, whose minuscule test tubes
and pipettes gleamed in the torchlight. He absorbedly transferred the
reddish fluid to a miniature filter-barrel, piercing a self-healing
plastic cover to do so. He said:

"You're pre-med? The way you talk--"

"I was an interne," said Kim. "Now I'm pre-corpse."

"I doubt that last," said Calhoun. "But I wish I had some distilled
water--This is anticoagulant." He added the trace of a drop to the
sealed, ruddy fluid. He shook the whole filter to agitate it. The
instrument was hardly larger than his thumb. "Now a clumper--" He added
a minute quantity of a second substance from an almost microscopic
ampule. He shook the filter again. "You can guess what I'm doing.
With a decent lab I'd get the structure and formula of the antibody
Murgatroyd has so obligingly turned out for us. We'd set to work to
synthesize it. In twenty hours, lab time, we ought to have it coming
out of the reaction-flasks in quantity. But there is no lab."

"There's one in the city," said the gaunt young man hopelessly. "It was
for the colonists who were to come. And we were staffed to give them
proper medical care. When the plague came, our doctors did everything
imaginable. They not only tried the usual culture tricks, but they
cultured samples of every separate tissue in the fatal cases. They
never found a single organism--even in the electron microscopes--that
would produce the plague." He said with a sort of weary pride, "Those
who'd been exposed worked until they had it, then others took over.
Every man worked as long as he could make his brain work, though."

Calhoun squinted through the glass tube of the filter at the
sputtering torch.

"Almost clumped," he observed. Then he said, "Did you ever hear of a
man named Pasteur? One of his first discoveries was that one could get
an effectively pure culture of a pathogenic organism by giving the
disease to an experimental animal. Better ways were found later, but
one still expects a pure culture in a patient who has a disease really
badly. What did the lab turn up?"

Kim shook his head.

"Nothing. The bacteriological survey of the planet had been thorough.
Oral and intestinal flora were normal. Naturally, the local bacteria
couldn't compete with the strains we humans have learned to live with.
They couldn't symbiotize. So there wasn't anything unknown. There
wasn't any cause of the plague."

Calhoun began to work the filter plunger, by the wavering light of
the torch. The piston was itself the filter, and on one side a clear,
mobile liquid began very slowly to appear.

"Mutated standard bug? Still, if your doctors did cultures and couldn't
reproduce the disease--"

"They could pass it," said Kim bitterly, "but they could never find
what carried it! No pure culture would!"

       *       *       *       *       *

Calhoun watched the clear fluid develop on the delivery side of the
filtering piston. The job got done. There was better than twelve cubic
centimeters of clear serum on the delivery side, and an almost solid
block of clumped blood cells on the other. He drew off the transparent
fluid with a fine precision.

"We're doing biochemistry under far from aseptic conditions," he said
wryly, "but the work has to be done and we have to take the risk.
Anyhow, I'm getting a feeling that this isn't any ordinary plague. A
normal pathogenic organism should have been turned up by your doctors."

"It wasn't," said Kim.

"So," said Calhoun, "maybe it isn't one isolatable organism. Maybe
the disease-producing mechanism simply isn't there when you make pure
cultures of the separate strains of virus and microbe. Murgatroyd was
a pretty sick animal. I've only known of one previous case in which
a _tormal_ reacted as violently as Murgatroyd did. That one had us
sweating."

"If I were going to live," said Kim grimly, "I might ask what it was."

"Since you're going to," Calhoun told him, "I'll tell you though you
don't. It was a pair of organisms. Their toxins acted synergically
together. Separately they were innocuous. Together they were
practically explosive. That one was the devil to track down!"

He went back across the glade. Murgatroyd came skipping after him,
scratching at the anaesthetic patch on his hide, which he sometimes
seemed to notice not because it felt oddly, but because it did not feel
at all.

"You," said Calhoun briefly to Helen Jons, "you go first. This is an
antibody serum. You may itch afterward, but I doubt it. Your arm,
please."

She bared her rather pitifully thin arm. He gave her practically a
CC of fluid which--plus blood-corpuscles and some forty-odd other
essential substances--had been circulating in Murgatroyd's blood stream
not long since. The blood-corpuscles had been clumped and removed by
one compound plus the filter, and the anticoagulant had neatly modified
most of the others. In a matter of minutes, the lab kit had prepared as
usable a serum as any animal-using technique would produce. Logically,
the antibodies it contained should be isolated and their chemical
structure determined. They should be synthesized, and the synthetic
antibody-complex administered to plague-victims. But Calhoun faced a
small group of people doomed to die. He could only use his field kit
to produce a small-scale miracle for them. He could not do a mass
production job.

"Next!" said Calhoun. "Tell them what it's all about, Kim!"

The gaunt young man bared his own arm.

"If what he says is so, this will cure us. If it isn't so, nothing can
do us any harm!"

And Calhoun briskly gave them, one after another, the shots of what
ought to be a curative serum for an unidentified disease which he
suspected was not caused by any single germ, but by a partnership.
Synergy is an acting-together. Charcoal will burn quietly. Liquid
air will not burn at all. But the two together constitute a violent
explosive. This is analogous to synergy. The ancient simple drug sulfa
is not intoxicating. A glass of wine is not intoxicating. But the two
together have the kick of dynamite. Synergy, in medicine, is a process
in which when one substance with one effect is given in combination
with another substance with another effect, the two together have the
consequences of a third substance intensified to fourth or fifth or
tenth power.

       *       *       *       *       *

"I think," said Calhoun when he'd finished, "that by morning you'll
feel better--perhaps cured of the plague and only weak from failure
to force yourselves to take nourishment. If it turns out that way,
I advise you all to get as far away from the city as possible for a
considerable while. I think this planet is going to be repopulated. I
suspect that shiploads of colonists are on the way here now--but not
from Dettra, which built the city. And I definitely guess that, sick
or well, you're going to be in trouble if or when you contact the new
colonists."

They looked tiredly at him. They were a singular lot of people. Each
one seemed half-starved, yet their eyes had not the brightness of
suffering. They looked weary beyond belief, and yet there was not
self-neglect. They were of that singular human type which maintains
human civilization against the inertia of the race--because it drives
itself to get needed things done. It is not glamorous, this dogged part
of mankind which keeps things going. It is sometimes absurd. For dying
folk to wash themselves, when even such exertion calls for enormous
resolution, is not exactly rational. To help each other try to die with
dignity was much more a matter of self-respect than of intellectual
decision. But as a Med Ship man, Calhoun viewed them with some warmth.
They were the type that has to be called on when an emergency occurs
and the wealth-gathering type tends to flee and the low-time-sense part
of a population inclines to riot or loot or worse.

Now they waited listlessly for their own deaths.

"There's no exact precedent for what's happened here," explained
Calhoun. "A thousand years or so ago there was a king of France--a
country back on old Earth--who tried to wipe out a disease called
leprosy by executing all the people who had it. Lepers were a nuisance.
They couldn't work. They had to be fed by charity. They died in
inconvenient places and only other lepers dared handle their bodies.
They tended to throw normal human life out of kilter. That wasn't the
case here. The man I killed wanted you dead for another reason. He
wanted you dead right away."

The gaunt Kim Walpole said tiredly:

"He wanted to dispose of our bodies in a sanitary fashion."

"Nonsense!" snapped Calhoun. "The city's infected. You lived, ate,
breathed, walked in it. Nobody can dare use that city unless they know
how the contagion's transmitted, and how to counteract it. Your own
colonists turned back. These men wouldn't have landed if they hadn't
known they were safe!"

There was silence.

"If the plague is an intended crime," added Calhoun, "you are the
witnesses to it. You've got to be gotten rid of before colonists from
somewhere other than Dettra arrive here."

The dark-bearded man growled:

"Monstrous! Monstrous!"

"Agreed," said Calhoun. "But there's no interstellar government, now,
any more than there was a planetary government in the old days back on
Earth. So if somebody pirates a colony ready to be occupied, there's
no authority able to throw them out. The only recourse would be war.
And nobody is going to start an interplanetary war! Not with the bombs
that can be landed! If the invaders can land a population here, they
can keep it here. It's piracy, with nobody able to do anything to the
pirates." He paused, and said with irony: "Of course they could be
persuaded that they were wrong."

But that was not even worth thinking about. In the computation of
probabilities in human conduct, self-interest is a high-value factor.
Children and barbarians have clear ideas of justice due to them, but
no idea at all of justice due from them. And though human colonies
spread toward the galaxy's rim, there was still a large part of every
population which was civilized only in that it could use tools. Most
people still remained comfortably barbaric or childish in their
emotional lives. It was a fact that had to be considered in Calhoun's
profession. It bore remarkably on matters of health.

"So you'll have to hide. I think permanently," Calhoun told them. "But
in the morning, after I've checked on you people again, I think I'll
go into the city and see what I can do about it. Try to rest now. You
should all feel much better in the morning."

Kim Walpole said abruptly:

"You've been exposed to the plague. Have you protected yourself?"

"Not yet," acknowledged Calhoun. "Give me a quarter of a CC."

He handed the injector to the gaunt young man. He noted the precision
with which Kim handled it. Then he helped get the survivors of the
original group--there were six of them--to the leafy beds under the
shelters. They were very quiet--even more quiet than their illness
demanded. They were very polite. The old man and woman who had
struggled back to the glade together made an especial attempt to bid
Calhoun good night with the courtesy appropriate to city folk of
tradition.

Calhoun settled down to keep watch through the night. Murgatroyd
snuggled confidingly close to him. There was silence.

       *       *       *       *       *

But not complete silence. The night of Maris III was filled with tiny
noises, and some not so tiny. There were little squeaks which seemed
to come from all directions, including overhead. There were chirpings
which were definitely at ground-level. There was a sound like effortful
grunting somewhere in the direction of the rampart of hills. In the
lowlands there was a rumbling which moved very slowly from one place to
another. By its rate of motion, Calhoun guessed that a pack or herd of
small animals was making a night-journey and uttering deep-bass noises
as it traveled.

He debated certain grim possibilities. The man he'd killed had had
a ground-car key in his pocket. He'd probably come out in a powered
vehicle. He might have had a companion, and the method of hunting down
fugitives--successful, in his case--was probably well established. That
companion might come looking for him, so watchfulness was necessary.

Meanwhile--the plague. The idea of synergy was still most plausible.
Suppose the toxins--the poisonous metabolic products--of two separate
kinds of bacteria combined to lessen the ability of the blood to
carry oxygen and scavenge away carbon dioxide? It would be extremely
difficult to identify the pair, and the symptoms would be accounted
for. No pure culture of any organism to be found would give the
plague. Each, by itself, would be harmless. Only a combination of two
would be injurious. And if so much was assumed--why--if the blood
lost its capacity to carry oxygen, mental listlessness would be the
first symptom of all. The brain requires a high oxygen-level in its
blood-supply if it is to work properly. Let a man's brain be gradually,
slowly, starved of oxygen and all the noted effects would follow.
His other organs would slow down, but at a lesser rate. He would not
remember to eat. His blood would still digest food and burn away its
own fat--though more and more sluggishly--while his brain worked only
foggily. He would become only semiconscious, and then there would come
a time of coma when unconsciousness claimed him and his body lived on
only as an idling machine--until it ran out of fuel and died.

Calhoun tried urgently to figure out a synergic combination which
might make a man's blood cease to do its work. Perhaps only minute
quantities of the dual poison might be needed--like an antivitamin or
an antienzyme, or--

The invaders of the city were immune. Quite possibly the same
antibodies Murgatroyd had produced were responsible for their safety.
Somewhere, somebody had very horribly used the science of medicine to
commit a monstrous crime. But the science of medicine--

A savage idea came to Calhoun. Its practicality might depend on the
number of men in the city. But his eyes burned.

He heard a movement across the glade. He reached for his blaster. Then
he saw where the motion was. It was Kim Walpole, intolerably weary,
trudging with infinite effort to where Helen Jons lay. Calhoun heard
him ask heavily:

"You're all right?"

"Yes, Kim," said the girl softly. "I couldn't sleep. I'm ... wondering
if we can hope."

Kim did not answer.

"If we live--" said the girl yearningly, and stopped.

Calhoun felt that he ought to put his fingers in his ears. The
conversation was strictly private. But he needed to be on guard. So he
coughed, to give notice that he heard. Kim called to him across the
starlit glade.

"Calhoun."

"Yes," said Calhoun. "If you two talk, I suggest that you do it in
whispers. I want to listen, in case the man I killed had friends who'll
come looking for him. Did you get his blaster, by the way?"

"Yes," said Kim from the darkness across the way.

"Good!" said Calhoun. "Keep it. And against all medical ethics, I
advise you to use it freely if you find suitable targets. But now,
just talk quietly if you can."

He settled back. Murgatroyd stirred and cuddled closer against him
without wakening. There was the faintest possible murmuring of
voices where Kim Walpole and the girl Helen talked wistfully of the
possibility of hope.

Calhoun felt very lonely, despite the violent activities he foresaw for
the morrow. He almost envied Kim Walpole. But he could not have traded
places with him. It wouldn't have been a fair trade. Calhoun was quite
confident that--via Murgatroyd--the folk in the glade had a very fair
chance of living for some time yet.

His own chances, considering what he had to do, were more nearly zero.
Just about zero, when considered dispassionately.




                                   V

    "Very much of physical science is merely the comprehension of
    long-observed facts. In human conduct, there is a long tradition of
    observation, but a very brief record of comprehension. For example,
    human life in contact with other human lives follows the rules of
    other ecological systems. All too often, however, a man may imagine
    that an ecological system is composed only of things, whereas such
    a system operates through the actions of things. It is not possible
    for any part of an ecological complex to act upon the other parts
    without being acted upon, in its turn. So that it is singularly
    stupid--and singularly common--for an individual to consider human
    society as passive and unreactive, so that he may do what he pleases
    without a reaction as energetic as his action, and as well-directed.
    Moreover, probability--."

                                        _Probability and Human Conduct_
                                                             Fitzgerald


An hour after sunrise Calhoun's shoulder-pack was empty of food. The
refugees arose, and they were weak and ravenous. Their respiration
had slowed to normal. Their pulses no longer pounded. Their eyes were
no longer dull, but very bright. But they were in advanced states
of malnutrition, and only now were aware of it. Their brains were
again receiving adequate oxygen and their metabolism was at a normal
level--and they knew that they were starving.

Calhoun served as cook. He trudged to the spring that Helen described
and brought back water. While they sucked on sweet tablets from his
rations and watched with hungry eyes, he made soup from the dehydrated
rations he'd carried for Murgatroyd and himself. He gave it to them as
the first thing their stomachs were likely to digest.

He watched as they fed themselves. The elderly man and woman consumed
it delicately, looking at each other. The man with the broad dark beard
ate with enormous self-restraint. Helen fed the weakest oldest man,
between spoonfuls for herself, and Kim Walpole ate slowly, brooding.

Calhoun drew him aside.

"During the night," he said, "I got another lot of serum ready. I'm
leaving it with you, with an injector. You'll find other refugees. I
gave you massive doses. You'd better be stingy. Try half-CC shots."

"What about you?" demanded Kim.

Calhoun shrugged.

"You'd be surprised how much authority I have--when I can make it
stick," he said dryly. "As a Med Ship man I've authority to take
complete charge of any health emergency. You people have a hitherto
unknown plague here. That's one emergency. The present inhabitants of
the city haven't got it. That's another. So since I have authority and
reason to exercise it if I can, I'm going to the city to take a little
action."

"You'll be killed," said Kim.

"Possibly," admitted Calhoun. "But the number of chance happenings
that could favor me is very much greater than the number of breaks
that could favor the invaders. And there's the matter of colonists.
Prospective colonists. You're being hunted so hard that they must be
about due. They've probably been immunized against this plague, but
technically I shouldn't let them land on a plague-stricken planet."

Kim Walpole stared.

"You mean you'll try to stop them?"

"I shall try," said Calhoun, "to implement the authority vested in me
by the Med Service for such cases as this. The rules about quarantine
are rather strict."

"You'll be killed," said Kim, again.

Calhoun ignored the repeated prediction.

"That hunter found you," he observed, "because he knew that you'd have
to drink. So he found a brook and followed it up, looking for signs of
humans drinking from it. He found footprints about the spring. I found
his footprints there, too. That's the trick you'll use to find other
fugitives. But pass on the word not to leave tracks hereafter. For
other advice, I advise you to get all the weapons you can. Modern ones,
of course. You've got the blaster from the man I killed."

"I think," said Kim between his teeth, "that I'll get some more. If
hunters from the city do track us to our drinking places, I'll know how
to get more weapons!"

"Yes," agreed Calhoun, and added, "Murgatroyd made the antibodies
that cured you. As a general rule, you can expect antibody production
in your own bodies once an infection begins to be licked. In case of
extreme emergency, each of you can probably supply antibodies for a
fair number of other plague-victims. You might try serum from blisters
you produce on your skin. Quite often antibodies turn up there. I don't
guarantee it, but sometimes it works."

He paused. Kim Walpole said harshly:

"But you! Isn't there anything we can do for you?"

"I was going to ask you something," said Calhoun. He produced the
telephoto films of the city as photographed from space. "There's a
laboratory in the city--a biochemistry lab. Show me where to look for
it."

Walpole gave explicit directions, pointing out the spot on the photo.
Calhoun nodded. Then Kim said fiercely:

"But tell us something we can do! We'll be strong, presently! We'll
have weapons! We'll track down-stream to where hunters leave their
ground-cars and be equipped with them! We can help you!"

Calhoun nodded approvingly.

"Right. If you see the smoke of a good-sized fire in the city, and if
you've got a fair number of fairly strong men with you, and if you've
got ground-cars, you might investigate. But be cagey about it! Very
cagey!"

"If you signal we'll come," said Kim Walpole grimly, "no matter how few
we are!"

"Fine!" said Calhoun. He had no intention of calling on these weakened,
starveling people for help.

       *       *       *       *       *

He swung his depleted pack on his back again and slipped away from the
glade. He made his way to the spring, which flowed clear and cool from
unseen depths. He headed down the little brook which flowed away from
it. Murgatroyd raced along its banks. He hated to get his paws wet.
Presently, where the underbrush grew thickly close to the water's edge,
Murgatroyd wailed. "_Chee! Chee!_" And Calhoun plucked him from the
ground and set him on his shoulder. Murgatroyd clung blissfully there
as Calhoun followed down the stream bed. He adored being carried.

Two miles down, there was another cultivated field. This one was set
out to a gigantized root-crop, and Calhoun walked past shoulder-high
bushes with four-inch blue-and-white flowers. He recognized the
plants as of the family _solanaceae_--belladona was still used in
medicine--but he couldn't identify it until he dug up a root and found
a potato. But the six-pound specimen he uncovered was still too young
and green to be eaten. Murgatroyd refused to touch it.

Calhoun was ruefully considering the limitations of specialized
training when he came to the end of the cultivated field. There was
a highway. It was new, of course. City, fields, highways and all
the appurtenances of civilized life had been built on this planet
before the arrival of the colonists who were to inhabit it. It was
extraordinary to see such preparations for a population not yet on
hand. But Calhoun was much more interested in the ground-car he found
waiting on the highway, hard by a tiny bridge under which the brook he
followed flowed.

The key he'd taken from the hunter fitted. He got in and put Murgatroyd
on the seat beside him.

"These invaders, Murgatroyd," he observed, "must be in a bad way. A
newly-built city which was never occupied will be like an empty house.
There's no amusement or loot to be found in prowling it. They were
sent to take over the planet, and they've done it. But they've nothing
to do now, except hunt refugees--until their colonists arrive. I
suspect they're bored. We'll try to fix that!"

He set the ground-car in motion. Toward the city.

It was a full twenty miles, but he did not encounter a single other
vehicle. Presently the city lay spread out before him. He stopped and
surveyed the vast pile. It was a very beautiful city. Fifty generations
of architects on many worlds had played with stone and steel, groping
for the perfect combination of materials with design. This city was a
product of their tradition. There were towers which glittered whitely,
and low buildings which seemed to nestle on the vegetation-covered
ground. There were soaring bridges, and gracefully curving highways,
and park areas laid out and ready. There was no monotony anywhere.

The only exception to gracefulness was the sturdy landing grid itself,
half a mile high and a mile across, which was a lace-work of massive
steel girders with spider-thin lines of copper woven about in the
complex curves the creation of its force-field required. Inside it,
Calhoun could see the ship of the invaders. It had been brought down
inside the circular structure and was dwarfed by it. It gleamed there.

"And we," said Calhoun, "are going to look for a prosaic, probably
messy laboratory which people who make a sport of hunting
fellow-humans won't find amusing. Characters like these, Murgatroyd,
aren't interested in medical science. They consider themselves
conquerors. People have strange ideas!"

"_Chee!_" said Murgatroyd.

Calhoun spread out his photographs. Kim Walpole had marked where he
should go and a route to it. Having been in the city while it was
building, he knew even the service-lanes which, being sunken, were not
a part of the city's good looks.

"But our enemies," explained Calhoun, "will not deign to use such
grubby routes. They consider themselves aristocrats because they were
sent as conquerors, whose job it was to clean up the dead bodies
of their victims. I wonder what kind of swine are in power in the
planetary government which sent them?"

       *       *       *       *       *

He put away the photos and headed for the city again. He branched off
from the rural highway where a turn-off descended into a cut. This
low-level road was intended for loads of agricultural produce entering
the city. It was strictly utilitarian. It ran below the surface of the
park areas and entered the city without pride. It wound between rows of
service-gates, behind which waste matter was some day to be assembled
to be carted away for fertilizer on the fields. The city was very well
designed.

Rolling along the echoing sunken road, Calhoun saw, just once, a
ground-car in motion on a far-flung, cobwebby bridge between two tall
towers. It was high overhead. Nobody in it would be watching grubby
commerce-roads.

The whole affair was very simple indeed. Calhoun brought the car to a
stop beneath the overhang of a balconied building many stories high.
He got out and opened the gate. He drove the car into the cavernous,
so-far-unused lower part of the building. He closed the gate behind
him. He was in the center of the city, and his presence was unknown.

He climbed a new-clean flight of steps and came to the sections the
public would use. There were glassy walls which changed their look as
one moved between them. There were the lifts. Calhoun did not try to
use them. He led Murgatroyd up the circular ramps which led upward in
case of unthinkable emergency. He and Murgatroyd plodded up and up.
Calhoun kept count.

On the fifth level there were signs of use, while all the others had
that dusty cleanness of a structure which has been completed but not
yet occupied.

"Here we are," said Calhoun cheerfully.

But he had his blaster in his hand when he opened the door of the
laboratory. It was empty. He looked approvingly about as he hunted for
the storeroom. It was a perfectly equipped biological laboratory, and
it had been in use. Here the few doomed physicians awaiting the city's
population had worked desperately against the plague. Calhoun saw the
trays of cultures they'd made--dried up and dead, now. Somebody had
turned over a chair. Probably when the laboratory was searched by the
invaders, lest someone not of their kind remained alive in it.

He found the storeroom. Murgatroyd watched with bright eyes as he
rummaged.

"Here we have the things men use to cure each other," said Calhoun
oracularly. "Practically every one a poison save for its special use!
Here's an assortment of spores--pathogenic organisms, Murgatroyd.
One could start a plague with them. And here are drugs which are
synthesized nowadays, but are descended from the compounds found on
the spears of savages. Great helps in medicine. And here are the
anaesthetics--poisons, too. These are what I am counting on!"

He chose, very painstakingly. Dextrethyl. Polysulfate. The one marked
inflammable and dangerous. The other with the maximum permissible dose
on its label, and the name of counteracting substances which would
neutralize it. He burdened himself. Murgatroyd reached up a paw. Since
Calhoun was carrying something, he wanted to carry something, too.

They went down the circular ramp again. Calhoun searched once more in
the below-surface levels of the building. He found what he wanted--a
painter's vortex gun which would throw "smoke rings" of tiny
paint-droplets at a wall or object to be painted. One could vary the
size of the ring at impact from a bare inch to a three-foot spread.

Calhoun cleaned the paint gun. He was meticulous about it. He filled
its tank with dextrethyl brought down from the laboratory. He piled the
empty containers out of sight.

"This trick," he observed, as he picked up the paint gun again, "was
devised to be used on a poor devil of a lunatic who carried a bomb in
his pocket for protection against imaginary assassins. It would have
devastated a quarter-mile circle, so he had to be handled gently."

He patted his pockets. He nodded.

"Now we go hunting--with an oversized atomizer loaded with dextrethyl.
I've polysulfate and an injector to secure each specimen I knock over.
Not too good, eh? But if I have to use a blaster I'll have failed."

He looked out a window at the sky. It was now late afternoon. He went
back to the gate to the service road. He went out and piously closed it
behind him. On foot, with many references to the photomaps, he began to
find his way toward the landing grid. It ought to be something like the
center of the invaders' location.

       *       *       *       *       *

It was dark when he climbed other service stairs from the cellar of
another building. This was the communications center of the city.
It had been the key to the mopping-up process the invaders began on
landing. Its call board would show which apartments had communicators
in use. When such a call showed, a murder-party could be sent to
take care of the caller. Even after the first night, some individual
isolated folk might remain--perhaps unaware of what went on. So there
would be somebody on watch, just in case a dying man called for the
solace of a human voice while still he lived.

There was a man on watch. Calhoun saw a lighted room. Paint gun at the
ready, he moved very silently toward it. Murgatroyd padded faithfully
behind him.

Outside the door, Calhoun adjusted his curious weapon. He entered.
There was a man nodding in a chair before the lifeless board. When
Calhoun entered he raised his head and yawned. He turned.

Calhoun sprayed him with smoke rings--vortex rings. But the rings were
spinning fissiles of vaporized dextrethyl--that anaesthetic developed
from ethyl chloride some two hundred years before, and not yet bettered
for its special uses. One of its properties was that the faintest
whiff of its odor produced a reflex impulse to gasp. A second property
was that--like the ancient ethyl chloride--it was the quickest-acting
anaesthetic known.

The man by the call board saw Calhoun. His nostrils caught the odor of
dextrethyl. He gasped.

He fell unconscious.

Calhoun waited patiently until the dextrethyl was out of the way. It
was almost unique among vapors in that at room temperature it was
lighter than air. It rose toward the ceiling. Calhoun moved forward,
brought out the polysulfate injector, and bent over the unconscious
man. He did not touch him otherwise.

He turned and walked out of the room with Murgatroyd piously marching
behind him.

Outside, Calhoun said:

"As one medical man to another, maybe I shouldn't have done that! I
doubt these invaders have a competent physician among them. But even
he would be apt to think that that man had collapsed suddenly and
directly into the coma of the plague. That polysulfate's an assisting
anaesthetic. It's not used alone, because when you knock a man out with
it he stays out for days. It's used just below the quantity that would
affect a man, and then the least whiff of another anaesthetic puts him
under, and he can be brought out fast and he's better off all around.
But I've got this man knocked out! He'll stay unconscious for a week."

Murgatroyd piped, "_Chee!_"

"He won't die," said Calhoun grimly, "but he won't come out
fighting--unless somebody wakes him earlier. And of course, he is a
murderer!"

"_Chee!_" agreed Murgatroyd.

He reached up a furry paw and took hold of Calhoun's hand. They walked
out into the street together.

It is notorious that the streets of a city at night are ghostly and
strange. That is true of a city whose inhabitants are only asleep.
There is more and worse of eeriness in a deserted city, whose
inhabitants are dead. But a city which has never lived, which lies
lifeless under the stars because its people never came to live in
it--that has the most ghastly feel of all.

Calhoun and Murgatroyd walked hand in paw through such a place. That
the invaders felt the same eeriness was presently proved. Calhoun found
a place where a light shone and voices came out into the tiny, remote
night sounds of Maris III. Men were drinking in an unnecessarily small
room, as if crowding together to make up for the loneliness outside. In
the still night they made a pigmy tumult with their voices. They banged
drunkenly on a table and on the floor.

Calhoun stood in the doorway and held the paint-gun trigger down. He
traversed the room twice. Whirling rings of invisible vapor filled the
place. Men gasped.

Calhoun waited a long time, because he had put a great deal of
dextrethyl into a small space. But presently he went in and bent over
each man in turn, while Murgatroyd watched with bright, inquisitive
eyes. He arranged one figure so that it seemed to have been stricken
while bending over another, fallen companion. The others he carried
out, one at a time, and placed at different distances as if they had
fallen while fleeing from a plague. One he carried quite a long
distance, and left him with dusty knees and hands as if he had tried to
crawl when strength failed him.

"They'd have been immunized at pretty well the same time, before they
were shipped on this job," Calhoun told Murgatroyd. "It'll seem very
plaguelike for them to fall into comas nearly together. If I found
men like this, and didn't know what to do, I'd suspect that it was a
delayed-action effect of some common experience--like an immunization
shot. We'd better try the ship, Murgatroyd."

On the way he passed close to the control-building of the landing grid.
There was a light inside it, too. There were four men on watch. Two
remained inside, very, very still, when Calhoun went on. The others
seemed to have fled and collapsed in the act. They breathed, to be
sure. Their hearts beat solidly. But it would not be possible to rouse
them to consciousness.

Calhoun didn't get into the ship, though. A chance happening
intervened, which seemed an unfavorable one. Its port was locked and
his cautious attempt to open it brought a challenge and a blaze of
lights.

He fled for the side of the landing grid with blaster-bolts searing the
ground all about him. Murgatroyd leaped and pranced with him as he ran.




                                  VI

    "The probable complete success of a human enterprise which affects
    non-co-operating other human beings may be said to vary inversely
    as the fourth power of the number of favorable happenings necessary
    for complete success. This formula is admittedly empirical, but
    its accordance with observation is remarkably close. In practice,
    the probability of absolute, total success in any undertaking is
    negligible. For this reason, mathematics and sanity alike counsel
    the avoidance of complex plannings, and most especially of plans
    which must succeed totally to succeed at all."

                                        _Probability and Human Conduct_
                                                             Fitzgerald


When morning came, Calhoun very wryly considered the situation. He
couldn't know the actual state of things, to be sure. He'd been shot
at. But even so--though that fact did not allow his hopes to be
realized in every detail--the probability of a considerable success
remained. It was not likely that the invaders would ascribe the
finding of unconscious, stertoriously breathing members of their
number to Calhoun. Making men unconscious was not the kind of warfare
a plague-refugee would use. Still more certainly, it was not what the
invaders themselves would practice. To devise and spread a plague, of
course, was not beyond them. That had been done. But they would not
disable an enemy and leave him alive. They would murder him or nothing.
So when men of their group were found in something singularly close
to the terminal coma of the plague, they'd think them victims. They'd
guess that their supposed immunity was only to the early symptoms, not
to the final ones and death.

It should not be an encouraging opinion.

But this morning Calhoun found himself hungry. He looked remorsefully
at Murgatroyd.

"I gave our rations to those refugees," he said regretfully. "I took no
thought for the morrow--which has turned out to be today. I'm sorry,
Murgatroyd!"

Murgatroyd said nothing.

"Maybe," suggested Calhoun, "we can find some of these invaders at a
meal."

It was reckless, but recklessness was necessary in the sort of thing
Calhoun had started. He and Murgatroyd ventured out into the streets.
The emptiness of the city was appalling. If it had been dilapidated,
if it had been partly ruined--the emptiness might have seemed somehow
romantic. But every building was perfect. Each was complete but
desolately unused.

Calhoun spotted a ground-car at a distance, stopped before a long, low,
ground-hugging structure near the landing grid. It was perfectly suited
to be the headquarters of the strangers in the city. Calhoun considered
it for a long time, peering at it from a doorway.

"We shouldn't try it," he said at last. "But we probably will. If
we can make these characters so panic-stricken that they run out of
the city like the earlier refugees--it would be a highly favorable
happening. They might do it if their bosses were knocked out by what
they thought was the plague. And besides, we should get a meal out of
it. There'll be food in there."

He backtracked a long way. He darted across a road with Murgatroyd
scampering beside him. He stalked the building, approaching it behind
bushes, carrying the paint gun. He reached its wall. He began to crawl
around the outside to reach the doorway. He heard voices as he passed
the first windows.

"_But I tell you we're immune!_" cried a voice furiously. "_It can't be
the same thing those Dettrans died from! It can't! And there was that
man who ran from the ship last night--_"

Calhoun crawled on. Murgatroyd skipped. Calhoun heard an exclamation
behind him. He turned his head, and Murgatroyd was fifteen feet away
from the building-wall, and plainly visible to those inside. And he'd
been seen fleeing with Calhoun from the ship.

Calhoun swore softly. He ran. He reached the door before which a
ground-car stood. He wrenched it open and set the paint gun at work
firing a steady stream of vortex rings into the interior. He drew his
blaster and faced the outside world.

There was a crashing of glass. Somebody had plunged out a window.
There were rushing feet inside. They'd be racing toward this doorway
from within. But the hallway--anteroom--foyer--whatever was immediately
inside the door would be filled with dextrethyl vapor. Men would gasp
and fall.

A man did fall. Calhoun heard the crash of his body to the floor. But
also a man came plunging around the building's corner, blaster out,
searching for Calhoun. But he had to sight his target and then aim for
it. Calhoun had only to pull trigger. He did.

Shoutings inside the building. More rushing feet. More falls. Then
there was the beginning of the rasping snarl of a blaster, and then
a cushioned, booming, roaring detonation which was the explosive
dextrethyl vapor, ignited by it. The blast lifted the building's roof.
It shattered partitions. It blew every window out.

Calhoun sprinted for the ground-car. A blaster-bolt flashed past him.
He halted and deliberately traversed the building with the trigger held
down. Smoke and flame leaped up. At least one more invader crumpled.
Calhoun heard a voice yelling inside somewhere.

"_We're attacked! Those refugees are throwing bombs! Rally! Rally! We
need help!_"

It would be a broadcast call for assistance. Wherever men lolled or
loafed or tried desultorily to find something to loot, they would hear
it. Even the standby crew in the spaceship would hear it. Those who
repaired the grid-transformers Calhoun had burned out would hear it.
Men would come running. Hunters would come. Men in cars--

Calhoun snatched Murgatroyd to the seat beside him. He turned the key
and the tires screamed and he shot away.

       *       *       *       *       *

The highways were of course, superb. He raced forward, and the car's
communicator began to mutter as somebody in the undamaged part of the
building chattered that he'd gotten in a car and away. It described his
course. It commanded that he be headed off. It hysterically demanded
that he be killed, killed, killed--

Another voice took its place. This voice was curt and coldly furious.
It snapped precise instructions.

Calhoun found himself on a gracefully curving, rising road. He was
midway between towers when another car flashed toward him. He took his
blaster in his left hand. In the split second during which the cars
passed each other, he blasted it. There was a monster surge of smoke
and flame as the stricken car's Duhanne cell shorted and vaporized half
the metal of the car itself.

There came other voices. Somebody had sighted the explosion. The voice
in the communicator roared for silence.

"_You_," he rasped. "_If you got him, report yourself!_"

"_Chee-chee-chee!_" chattered Murgatroyd excitedly.

But Calhoun did not report.

"_He got one of us_," raged the icy voice. "_Get ahead of him! And
blast him!_"

Calhoun's car went streaking down the far side of the traffic-bridge.
It rounded a curve on two wheels. It flashed between two gigantic
empty buildings and came to a sideway, and plunged into that, and came
again to a division and took the left-hand turn, and next time took
the right. But the muttering voices continued in the communicator. A
voice, by name, was ordered to the highest possible bridge from which
it could watch all lower-level roadways. Others were to post themselves
here, and there--and to stay still! A group of four cars was coming out
of the storage-building. Blast any single car in motion. Blast it! And
report, report, report--

"I suspect," said Calhoun to the agitated Murgatroyd beside him, "that
this is what is known as military tactics. If they ring us in--There
aren't but so many of them, though. The trick for us is to get out of
the city. We need more choices for action. So--"

The communicator panted a report of his sighting, from a cobweblike
bridge at the highest point of the city. He was heading--

He changed his heading. He had so far seen but one car of his pursuers.
Now he went racing along empty, curving highways, among untenanted
towers and between balconied walls with blank-eyed windows gazing at
him everywhere.

It was nightmarish because of the magnificence and the emptiness of
the city all about him. He plunged along graceful highways, across
delicately arched bridges, through crazy ramifications of its lesser
traffic arteries--and he saw no motion anywhere. The wind whistled
past the car windows, and the tires sang a high-pitched whine, and the
sun shone down and small clouds floated tranquilly in the sky. There
was no sign of life or danger anywhere on the splendid highways or in
the heart-wrenchingly beautiful buildings. Only voices muttered in the
communicator of the car. He'd been seen here, flashing around a steeply
banked curve. He'd swerved from a waiting ambush by pure chance. He'd--

He saw green to the left. He dived down a sloping ramp toward one of
the smaller park areas of the city.

And as he came from between the stone guard rails of the road, the top
of the car exploded over his head. He swerved and roared into dense
shrubbery, jerked Murgatroyd free despite the _tormal's_ clinging fast
with all four paws and his tail, and dived into the underbrush.

       *       *       *       *       *

He ran, swearing and plucking solidified droplets of still-hot metal
from his garments and his flesh. They hurt abominably. But the man
who'd fired wouldn't believe he'd missed, followed as his blasting was
by the instant wrecking of the car. The man who'd fired would report
his success before he moved to view the corpse of his supposed victim.
But there'd be other cars coming. At the moment it was necessary for
Calhoun to get elsewhere, fast.

He heard the rushing sound of arriving cars while he panted and sweated
through the foliage of the park. He reached the far side and a road,
and on beyond there was a low stone wall. He knew instantly what it
was. Service highways ran in cuts, now and again roofed over to hide
them from sight, but now and again open to the sky for ventilation.
He'd entered the city by one of them. Here was another. He swung
himself over the wall and dropped. Murgatroyd recklessly and excitedly
followed.

It was a long drop, and he was staggered when he landed. He heard a
soft rushing noise above. A car raced past. Instants later, another.

Limping, Calhoun ran to the nearest service-gate. He entered and closed
it. Scorched and aching, he climbed to the echoing upper stories of
this building. Presently he looked out. His car had been wrecked in one
of the smaller park areas of the city. Now there were other cars at
two-hundred-yard intervals all about it. It was believed that he was
in the brushwood somewhere. Besides the cars of the cordon, there were
now twenty men on foot receiving orders from an authoritative figure in
their midst.

They scattered. Twenty yards apart, they began to move across the park.
Other men arrived and strengthened the cordon toward which he was
supposed to be driven. A fly could not have escaped.

Those who marched across the park began methodically to burn it to
ashes before them with their blasters.

Calhoun watched. Then he remembered something and was appalled. Among
the fugitives in the glade, Kim Walpole had asked hungrily if they
whose lives he had saved could not do something to help him. And he'd
said that if they saw the smoke of a good-sized fire in the city they
might investigate. He'd had no faintest intention of calling on them.
But they might see this cloud of smoke and believed he wanted them to
come and help!

"Damn!" he said wryly to Murgatroyd. "After all, there's a limit to
any one series of actions with probable favorable chance consequences.
I'd better start a new one. We might have whittled them down and made
the unwhittled ones run away, but I had to start using a car! And then
they'd try to blame me for everything. So--we start all over with a new
policy."

He explored the building quickly. He prepared his measures. He went
back to the window from which he'd looked. He cracked its window.

He opened fire with his blaster. The range was long, but with the beam
cut down to minimum spread he'd knocked over a satisfying number of the
men below before they swarmed toward the building, sending before them
a barrage of blaster-fire that shattered the windows and had the stone
façade smoking furiously.

"This," said Calhoun, "is an occasion where we have to change their
advantage in numbers and weapons into an unfavorable circumstance for
them. They'll be brave because they're many. Let's go!"

       *       *       *       *       *

He met the two ground-car loads of refugees with his arms in the air.
He did not want to be shot down by mistake. He said hurriedly, when Kim
and the other lean survivors gathered about him:

"Everything's all right. We've a pack of prisoners but we won't
bother to feed them intravenously for the moment. How'd you get the
ground-cars?"

"Hunters," said Kim savagely. "We found them and killed them and took
their cars. We found some other refugees, too, and I cured them--at
least they will be cured. When we saw the smoke we started for the
city. Some of us still have the plague, but we've all had our serum
shots." His face worked. "When we started for the city, another car
overtook us. Naturally he wasn't suspicious of a car! We blasted him.
Half of us have arms, now."

"I don't think we need them," said Calhoun. "Our prisoners are quite
peacefully sleeping. They stormed a building where I'd fired on them,
and I'd dumped some dextrethyl in the air-conditioning system. They
keeled over. Later, Murgatroyd and I went in and made their slumber
more ... ah ... lasting with polysulfate. The few who weren't caught
were ... ah ... demoralized. I think the city's clean, now. But we've
got to get to the landing-grid control room. There are some calls
coming in from space. I think the first shipload of colonists is
arriving. I didn't answer, so they went in orbit around the planet. I
want you people to talk to them."

"We'll bring their ship down," said the bearded man hungrily, "and
blast them as they come out the exit port!"

Calhoun shook his head.

"To the contrary," he said regretfully. "You'll put on the clothes of
some of our prisoners. You'll tell the arriving colonists that the
plague hit you, too. You'll pretend to be one of the characters we
really have safely sleeping, and you'll say all the rest have been
bowled over by the plague that was sowed here to win the planet for the
characters you're talking to. If they land, they'll die--or so you'll
tell them. And so they will all go home, very unhappy, and they'll tell
the public about it. And there will be no more shiploads of colonists
arriving. We don't want them. If we persuade them to go home and not
come back, there are fewer chances of unfavorable consequences to us."

The bearded man growled. But later he was one of the most convincing
of the scarecrow figures whose images appeared in the vision-plates of
the ship overhead. He was especially pathetic and alarming. When he'd
finished, there'd have been a mass mutiny of the passengers had the
spaceship skipper tried to land them.

Later, all the fugitives were very conscientious about bringing the
captive invaders out of the lethargy that had been begun by dextrethyl
and reinforced by polysulfate. They enjoyed their labor, after Calhoun
explained.

"They came in their own ship," he said mildly, "and it's still in
the landing grid--which they repaired for us, by the way. And I've
been aboard the ship with Kim, here, and we've smashed their drive
and communicators, and wrecked their Duhanne circuits. We took out
the breech-plugs of their rockets and dumped their rocket fuel. Of
course we removed their landing boats. So we're going to put them in
their ship and hoist them up to space with the landing grid, and we're
going to set them in a lovely orbit, to wait until we've time to spare
for them. Up there they can't run or land or even signal if another
shipload of colonists turns up. They'll feed themselves and they won't
need guarding, and they'll be quite safe until we get help from Dettra.
And that will come as soon as the Med Service has told Dettra that it
wasn't a plague but an invasion that seemed to take their colony away
from them."

"But--" That was Kim Walpole, frowning.

"I'm bringing my ship to the grid," said Calhoun, "and we'll recharge
my Duhanne cells and replace my vision screens. I can make it here on
rocket power, but it's a long way back to Headquarters. So I'll report,
and a field team will come here from Med Service to get the exact data
on the plague, and just how the synergy factor worked, and to make
everything safe for the people the city was built for. Incidentally,
I've a tiny blood-sample from Helen that they can get to work on for
the bacteriology."

Kim said, frowning:

"I wish we could do something for you!"

"Put up a statue," said Calhoun dryly, "and in twenty years nobody
will know what it was for. You and Helen are going to be married,
aren't you?" When Kim nodded, Calhoun said, "In course of time, if you
remember and think it worth while, you may inflict a child with my
name. That child will wonder why, and ask, and so my memory will be
kept green for a full generation!"

"Longer than that!" insisted Kim. "You'll never be forgotten here!"

Calhoun grinned at him.

       *       *       *       *       *

Three days later, which was six days longer than he'd expected to be
aground on Maris III, the landing grid heaved the little Med Ship out
to space. The beautiful, nearly-empty city dwindled as the grid-field
took the tiny spacecraft out to five planetary diameters and there
released it. And Calhoun spun the Med Ship about and oriented it
carefully for that place in the Cephis cluster where Med Service
Headquarters was, and threw the overdrive switch.

The universe reeled. Calhoun's stomach seemed to turn over twice, and
he had a sickish feeling of spiraling dizzily in what was somehow a
cone. He swallowed. Murgatroyd made gulping noises. There was no longer
a universe preceptible about the ship. There was dead silence. Then
those small random noises began which have to be provided if a man is
not to crack up in the dead stillness of a ship traveling at thirty
times the speed of light.

Then there was nothing more to do. In overdrive travel there is never
anything to do but pass the time away.

Murgatroyd took his right-hand whiskers in his right paw and licked
them elaborately. He did the same to his left-hand whiskers. He
contemplated the cabin, deciding upon a soft place in which to go to
sleep.

"Murgatroyd," said Calhoun severely, "I have to have an argument with
you! You imitate us humans too much! Kim Walpole caught you prowling
around with an injector, starting to give our prisoners another shot of
polysulfate! It might have killed them! Personally, I think it would
have been a good idea, but in a medical man it would have been most
unethical. We professional men have to curb our impulses! Understand?"

"_Chee!_" said Murgatroyd. He curled up and wrapped his tail
meticulously about his nose, preparing to doze.

Calhoun settled himself comfortably in his bunk. He picked up a book.
It was Fitzgerald on "Probability and Human Conduct."

He began to read as the ship went on through emptiness.


                                THE END