The crescent which was the planet Kryder II enlarged gradually, with the sun many millions of miles beyond it. The Aesclipus Twenty swung in its course, pointing at a right angle to the line along which it had been moving. Its drive-baffles glowed faintly as the Lawlor interplanetary drive gave it a new impetus, changing its line of motion by adding velocity in a new direction to the sum of all the other velocities it had acquired. Then the ship swung back, not quite to its former bearing but along the line of its new course.
Inside the ship, Calhoun again aimed the ship. He used the sighting circle at the very center of the dead-ahead vision screen. He centered a moderately bright star in that glowing circle. The star was a certain number of seconds of arc from the planet's sunlit edge. Calhoun watched. All about, in every direction, multitudes of shining specks—actually suns—floated in space. Many or most of them warmed their families of planets with the solicitude of brooding hens. Some circled each other in stately, solemn sarabands. There were some, the Cepheids, which seemed to do neither but merely to lie in emptiness, thin and gaseous, pulsating slowly as if breathing.
Calhoun relaxed, satisfied. The guide star remained at exactly the same distance from the crescent planet, while the Med Ship hurtled toward it. This arrangement was a standard astrogational process. If the moving planet and the sighting star remained relatively motionless, the total motion of the Med Ship was exactly adjusted for approach. Of course, when close enough the relationship would change, but if the ship's original line was accurate, the process remained a sound rule-of-thumb method for approaching a planet.
The Med Ship sped on. Calhoun, watching, said over his shoulder to Murgatroyd, "We're pretty much in the dark about what's going on, Murgatroyd, not in the matter of the plague, of course. That's set up to be ended by somebody arriving in a Med Ship, as in two cases before this one. But if they can end it, they needn't have started it. I don't like the idea of anything like this being unpunished."
Murgatroyd scratched reflectively. He could see the vision screens. He could have recognized buildings as such, though probably not as individual ones. On the screens, save for the sun and one crescent planet, there were only dots of brightness of innumerable colorings. To Murgatroyd, who spent so much of his life in space travel, the stars had no meaning whatever.
"Technically," observed Calhoun, "since medicine has become a science, people no longer believe in plague-spreaders. Which makes spreading plagues a possible profession." *
Murgatroyd began to clean his whiskers, elaborately licking first the right-hand and then the left-hand ones.
Calhoun again checked the relative position of the sighting star and Kryder II. He brought up a file on the computer. It was a resume of the history of toxicology. He hunted busily for items having to do with the simulation of bacterial toxins by inorganic compounds. He made notes, not many. He consulted another file. It dealt with antigens and antibodies. He made more notes and consulted a third file.
He worked carefully with pencil and paper and then, with his memos at hand, Calhoun set the computer to find the known compounds with such-and-such properties, a boiling point above so-and-so, with an inhibitive effect upon the formation of certain other compounds.
He went back to the pilot's chair. The crescent world was noticeably nearer and larger. Calhoun became absorbed in the delicate task of putting the Med Ship in suitable orbit around Kryder II. The ship obeyed him. It swung around to the green world's sunlit hemisphere. He addressed the communicator microphone:
"Med Ship Aesclipus Twenty calling ground to report arrival and ask coordinates for landing. Our mass is fifty standard tons. Repeat, five-oh tons. Purpose of landing . . . response to planetary health department request for service."
Calhoun watched as more of the surface of the nearing planet came into view with the Med Ship's swing around it. There were bright green continents, showing irregular streaks of white glaciation where mountain ranges rose. There were seas and oceans and cloud masses and that filmy blue haze at the horizon which so much surprised the first explorers of space.
"Med Ship Aesclipus—" Calhoun's recorded voice repeated the call. Murgatroyd popped his head out of his personal cubbyhole. When Calhoun talked, but not to him, it meant that presently there would be other people around. And people did not long remain strangers to Murgatroyd. He made friends with ease and zest. Except for Calhoun, Murgatroyd defined friends as people who gave him sweet cakes and coffee.
The communicator speaker said, "Calling Med Ship! Ground calling Med Ship! Coordinates are . . ." the voice named them. It sounded warm and even rejoicing through the speaker, as if the landing-grid operator had a personal interest in the arrival of a man sent by the Interstellar Medical Service. "We're plenty glad you've come, sir! Plenty glad! Did you get the coordinates? They're . . ."
"Chee!" said Murgatroyd zestfully.
He clambered down to the control-room floor and looked at the screen. When Calhoun spoke again to the grid operator, Murgatroyd strutted. He would land, and he would be the center of attention everywhere so long as the Med Ship was aground. He practically crooned his delight.
"Yes, sir!" said the voice from the ground. "Things were looking pretty bad! There's a Doctor Kelo here, sir. He was on Castor IV when they had a plague there. He says the Med Service man that came there got it licked right off. Excuse me, sir. I'm going to report you're coming in."
The voice stopped. Calhoun glanced at the coordinates he'd written down and made adjustment for the Med Ship's needed change of course. It was never necessary to be too precise in making a rendezvous with a landing grid. A ship had to be several planetary diameters out from ground to have even its interplanetary drive work. But a grid's force fields at so many thousands of miles distance were at first widely spread and tenuous. They reported to ground when they first touched the incoming ship. Then they gathered together and focused on the spacecraft, and then they tightened and grew strong. After that they pulled the ship down gently out of emptiness to the center of that half-mile-high circle of steel girders and copper cable which was the landing grid. It took time to pull a ship down some thousands of miles. Too violent a pull could be disastrous to the crew, but ordinarily it was marvelously effective and totally safe.
The communicator screen swirled suddenly and then presented a very clear picture of the grid-control office. It showed the operator. He gazed admiringly at Calhoun.
"I've reported, sir," he said warmly, "and Doctor Kelo's coming right now! He was at the big hospital, where they've been working on what the plague can be. He's coming by copter . . . won't be long."
Calhoun reflected. According to his data, Doctor Kelo had been a prominent physician on Castor IV when the Med Ship man there had presumably been killed in the detonation of the ship. Doctor Kelo had made a report on that matter. The two men who'd come to take over the Med Ship at its breakout point, not an untold number of hours ago, had read his report with seeming amusement. They'd noted Doctor Kelo's name. It was at least interesting that this same Doctor Kelo was here, where there also was a plague. However, the Med Ship man he expected wasn't Calhoun. Calhoun was supposed to be floating somewhere in emptiness, light-hours away from here.
The grid operator watched his dials. He said, pleased, "Got it, sir! Fifty tons, you said. I'll lock on."
Calhoun felt the curious fumbling sensation the grid's force fields produced when they touched and gathered around the ship, and then the cushiony thrustings and pushings when the fields focused and intensified. The Aesclipus Twenty began its descent.
"I'll bring you down now, sir," said the operator of the grid, very happily. "I'll make it as quick as I can, but you're a long way out!"
Landing was bound to be a lengthy process, much longer than lifting off. One could not snatch a ship from space. It had to be brought down with no more acceleration planetward than a ship's company could endure. Eventually the downward speed had to be checked so the contact with the ground would be a gentle one. A grid could smash a ship to atoms by bringing it down on the spaceport tarmac with a velocity of miles per second. This was why interplanetary wars were impossible. A landing grid could smash any ship in space if it approached a planet with hostile intentions.
"I suppose," said Calhoun, "there's a lot of concern about the—epidemic. The planetary health department asked for me."
"Yes, sir! It's real bad! Started three months ago. There were half a dozen cases of pneumonia. Nobody thought much about it. They were treated, and stopped having pneumonia, but they weren't well. They had something else, not the same thing, either. There was typhoid and meningitis and so on. This is what the newscasts say. Then other cases turned up. A child would have measles, and it would turn to tetanus, and that to pneumonia, and that to scarlet fever. . . . It couldn't happen, the doctors said, but it was happening! The hospitals filled up. More came in all the time, and none of them could leave. They could keep most of the cases alive, but they had to cure 'em of something else all the time. They had to turn schools and churches into hospitals. One person in ten is sick already. More are taken down every minute. Presently, there won't be doctors enough to diagnose the diseases patients contract continually. They figure that a quarter of the whole population will be down inside of two weeks more, and then they'll start dying faster than they do now, because there won't be enough well people to take care of 'em. They figure there won't be anybody on his feet in a month and a half from now and that'll be the end for everybody."
Calhoun clamped his jaws together.
"They've stopped giving it out," said the grid operator. He added professionally, "I've got you coming down at four hundred feet a second, but I'm going to pull a lot harder! You're needed down here in a hurry! I'll put on the brakes at a thousand miles, and you'll touch ground like a feather."
Calhoun ground his teeth. Strictly speaking, he should discuss the plague only with qualified medical men. But the public attitude toward a disease has to be considered in its treatment. This, however, was plainly not a disease. A given bacterium or virus can produce one disease only. Its activity may vary in virulence, but not in kind. Viruses do not change to bacteria. Cocci do not change to spirochetes. Each pathogenic organism that exists remains itself. It may change in viciousness, but never in form. The plague as described could not be a plague! It could not be!
Immediately one ceased to think of it as a natural plague; immediately one considered it artificial, it made sense. It tended to spread toward a total, cent-percent matching of number of cases to the number of people on the planet. Normal pestilences do not. It was planned that a fake Med Ship man should arrive at a certain time and end it. This would be absurd if the plague were a natural one. It was the third of its kind, and the first two had killed tormals—which pestilences could not—and in each case large sums of money had disappeared.
"Doctor Kelo, sir," said the grid operator, said he was sure that if a Med Ship man could get here with his—what's that little creature? A tormal? Once a Med Ship man got here with his tormal, the plague was as good as licked." He stopped and listened. "Doctor Kelo must be here now. There's a copter landing outside."
Then the grid man said with a rather twisted grin, "I tell you, everybody's glad you're here! I've got a wife and kids. They haven't got the plague yet, but . . ."
He stood up. He said joyously, "Doctor Kelo! Here he is! Right here on the screen! We've been talkin'. He's comin' down fast, and I'll have him aground in a hurry!"
A voice said, "Ah, yes! I am most pleased. Thank you for notifying me."
Then a new figure appeared on the vision screen. It was dignified. It was bearded. It was imposing in the manner of the most calmly confident of medical men. One could not look at Doctor Kelo without feeling confidence in him. He seemed benign. He beamed at the grid man and turned to the vision screen.
He saw Calhoun. Calhoun regarded him grimly. Doctor Kelo stared at him. Calhoun was not the man who'd been put aboard the Med Ship at first breakout point. He wasn't the man who'd handled the Castor IV epidemic, or the one before that. He wasn't the man who was supposed to have been killed when a Med Ship blew up in the Castor IV spaceport. He wasn't . . .
"How do you do?" said Calhoun evenly. "I gather we are to work together—again, Doctor Kelo."
Doctor Kelo's mouth opened, and shut. His face went gray. He made an inarticulate sound. He stared at Calhoun in absolute stupefaction. Murgatroyd squirmed past Calhoun's body to look into the communicator screen. He saw a man, and to Murgatroyd that meant that shortly he would be aground among people who admired him adoringly and would therefore stuff him with all the things he liked to eat and drink.
"Chee!" said Murgatroyd cordially. "Chee-chee!"
The stark incredulity of the bearded face changed to shock. That expression became purest desperation. One of Doctor Kelo's beautifully manicured hands disappeared. It appeared again. There was a tiny snapping sound and the grid operator became suddenly boneless. He seemed to bend limply in all his joints and almost to pour downward to the floor.
Doctor Kelo turned swiftly to the dials of the landing-grid control-board. He surveyed them, panting suddenly. Of course, a landing grid can do its work in many different fashions. It can use the processes of normal space commerce to make space war impossible. Because it can be deadly.
Doctor Kelo reached out. Calhoun could not see exactly what he did, but he could guess its purpose. Immediately he felt a surging of the Med Ship which told him exactly what had been done. It was an increased downward velocity of the ship, which had to be brought down rapidly for most of its descent, or otherwise the grid would swing around to the night side of this world where, with a planet's bulk between, it could not do anything with the Med Ship at all. However, high acceleration toward the ground could be used to a certain point only. Below a critical distance the ship couldn't be stopped. It would be bound to crash to flaming destruction against the world it had meant to land on.
The ship surged again. It plunged planetward with doubled acceleration. In the grip of the landing grid's force fields, it built up to a velocity far beyond any at which it could be slowed for a safe landing. It was building up toward the speed of shooting stars, which consume themselves when they touch atmosphere. It was still thousands of miles out in emptiness, still speeding crazily to inevitable destruction.