Peter Karson was dead. He had been dead for some time now, but the dark blood was still oozing from the crushed ruin of his face, trickling down into his sodden sleeve, and falling, drop by slow drop, from his fingertips. His head was tilted over the back of the chair at a queer, unnatural angle, so that the light made deep pools of shadow where his eyes had been.

There was no sound in the room except for the small splashing the blood made as it dropped into the sticky pool on the floor. The great banks of machinery around the walls were silent. I knew that they would never come to life again.

I rose and walked over to the window. Outside, the stars were as before: tiny, myriad points of light, infinitely far away. They had not changed, and yet they were suddenly no longer friendly. They were cold and alien. It was I who had changed: something inside me was dead, like the machinery, and like Peter.

It was a kind of indefinable emptiness. I do not think it was what Peter called an emotion; and yet it had nothing to do with logic, either. It was just an emptiness—a void that could not be filled by eating or drinking.

It was not a longing. I had no desire that things should be otherwise than they were. I did not even wish that Peter were not dead, for reason had told me that he had to die. That was the end of it.

But the void was still there, unexplainable and impossible to ignore. For the first time in all my life I had found a problem that I could not solve. Strange, disturbing sensations stirred and whispered within me, nagging, gnawing. And suddenly—something moved on the skin of my cheek. I raised a hand to it, slowly.

A tear was trickling down my cheek.

Young Peter Karson put the last black-print down and sighed with satisfaction. His dream was perfect; the Citadel was complete, every minutest detail provided for—on paper. In two weeks they would be laying the core, and then the metal giant itself would begin to grow, glittering, pulsing with each increment of power, until at last it lay finished, a living thing.

Then there would remain only the task of blasting the great, shining ship out into the carefully-calculated orbit that would be its home. In his mind's eye he could see it, slowly wheeling, like a second satellite, about the Earth; endlessly gathering knowledge into its insatiable mechanisms. He could see, too, the level on level of laboratories and storerooms that filled its interlocking segments; the meteor deflectors, the air renewal system, the mighty engines at the stern—all the children of his brain.

Out there, away from the muffling, distorting, damnable blanket of atmosphere, away from Earth's inexorable gravitational pull, would be a laboratory such as man had never seen. The ship would be filled with the sounds of busy men and women, wresting secrets from the reluctant ether. A new chemistry, a new physics; perhaps even a new biochemistry.

A discordant note suddenly entered his fantasy. He looked up, conscious of the walls of his office again, but could see nothing unusual. Still, that thin, dark whisper of dread was at the back of his mind. Slowly, as if reluctantly compelled, he turned around to face the window at his back.

There, outside the window, fifty stories up, a face was staring impassively in at him. That was the first impression he got; just a face, staring. Then he saw, with a queer, icy chill, that the face was blood-red and subtly inhuman. It tapered off into a formless, shriveled body.

For a moment or an eternity it hung there, unsupported, the bulging eyes staring at him. Then it grew misty at the edges. It dissolved slowly away and was gone.

"Lord!" he said.

He stared after it, stunned into immobility. Down in the street somewhere, a portable video was shrilling a popular song; after a moment he heard the faint swish of a tube car going past. Everything was normal. Nothing, on examination, seemed to have changed. But the world had grown suddenly unreal.

One part of his brain had been shocked into its shell. It was hiding from the thing that had hurt it, and it refused to respond. But the other part was going calmly, lucidly on, quite without his volition. It considered the possibility that he had gone temporarily insane, and decided that this was probable.

Hardly knowing what he did, he found a cigarette and lit it. His hands were shaking. He stared at them dully, and then he reached over to the newsbox on his desk, and switched it on.

There were flaring red headlines.

Relief washed over him, leaving him breathless. He was horrified, of course, but only abstractedly. For the moment he could only be glad that what he had seen was terrible reality rather than even more terrible illusion.

INVADERS APPEAR IN BOSTON.
200 DEAD

Then lines of type, and farther down:

50 CHILDREN DISAPPEAR FROM
PARIS MATERNITY CENTER

He pressed the stud. The roll was full of them.

MOON SHIP DESTROYED
IN TRANSIT
NO COMMUNICATION FROM
ANTARCTICA IN 6 HOURS
STRANGE FORCE DEFLECTS
PLANES FROM SAHARA AREA
WORLD POLICE MOBILIZING

The item below the last one said:

Pacifica, June 7—The World Police are mobilizing, for the first time in fifty years. The order was made public early this morning by R. Stein, Secretary of the Council, who said in part:

"The reason for this ... order must be apparent to all civilized peoples. For the Invaders have spared no part of this planet in their depredations: they have laid Hong Kong waste; they have terrorized London; they have destroyed the lives of citizens in every member state and in every inhabited area. There can be few within reach of printed reports or my words who have not seen the Invaders, or whose friends have not seen them.

"The peoples of the world, then, know what they are, and know that we face the most momentous struggle in our history. We face an enemy superior to ourselves in every way.

"Since the Invaders first appeared in Wood River, Oregon, 24 hours ago, they have not once acknowledged our attempts to communicate, or in any way taken notice of our existence as reasoning beings. They have treated us precisely as we, in less enlightened days, might have treated a newly-discovered race of lower animals. They have not attacked our centers of government, nor immobilized our communications, nor laid siege to our defenses. But in instance after instance, they have done as they would with us. They have examined us, dissected us, driven us mad, killed us with no discernable provocation; and this is more intolerable than any normal invasion.

"I have no fear that the people of Earth will fail to meet this challenge, for there is no alternative. Not only our individual lives are threatened, but our existence as a race. We must, and will, destroy the Invaders!"

Peter sank back in his chair, the full shock of it striking him for the first time.

"Will we?" he asked himself softly.

It was only two stories down the moving ramp to Lorelei Cooper's laboratory. Peter took it in fifteen seconds, running, and stumbled to a halt in front of the door marked "Radiation." She had set her door mechanism to "Etaoin Shrdlu," principally because he hated double-talk. He mouthed the syllables, had to repeat them because he put an accent in the wrong place, and squeezed through the door as soon as it opened far enough to admit him.

Lorelei, beautiful in spite of dark-circled eyes and a smear of grease on her chin, looked up from a huge ledger at the end of the room. One blonde eyebrow arched in the quizzical expression he knew so well.

"What makes, Peter my love?" she asked, and bent back to the ledger. Then she did a double-take, looked at his face intently, and said, "Darling, what's wrong?"

He said, "Have you seen the news recently?"

She frowned. "Why, no—Harry and I have been working for thirty-six hours straight. Haven't seen anybody, haven't heard anything. Why?"

"You wouldn't believe me. Where's your newsbox?"

She came around the desk and put her hands on his shoulders. "Pete, you know I haven't one—it bores me or upsets me, depending on whether there's trouble or not. What—"

"I'm sorry, I forgot," he said. "But you have a scanner?"

"Yes, of course. But really, Pete—"

"You'll understand in a minute. Turn it on, Lorelei."

She gazed at him levelly for a moment, kissed him impulsively, and then walked over to the video panel on the wall and swept a mountain of papers away from in front of it. She turned the selector dial to "News" and pressed the stud.

A faint wash of color appeared on the panel, strengthened slowly, and suddenly leapt into full brilliance.

Lorelei caught her breath.

It was a street scene in the Science City of Manhattan, flooded by the warm spring sunshine. Down on the lowest level, visible past the transport and passenger tubes, the parks and moving ways should have been dotted with colorful, holiday crowds. The people were there, yes but they were flowing away in a swiftly-widening circle. They disappeared into buildings, and the ways snatched them up, and in a heartbeat they were gone.

There were left only two blood-red, malignant monstrosities somehow defiling the air they floated in; and below them, a pitiful huddle of flesh no longer recognizable as human beings. They were not dead, those men and women, but they wanted to be. Their bodies had been impossibly joined, fused together into a single obscene, floundering mass of helpless protoplasm. The thin moaning that went up from them was more horrible than any cry of agony.

"The Invaders are here, citizens," the commentator was saying in a strangled voice. "Stay off the streets. Hide yourselves. Stay off the streets...." His voice droned on, but neither of them heard it.

Lorelei buried her head on his chest, clutching at him desperately. "Peter!" she said faintly. "Why do they broadcast such things?"

"They have to," he told her grimly. "There will be panics and suicides, and they know it; but they have to do it. This isn't like a war, where the noncombatants' morale has to be kept up. There aren't going to be any noncombatants, this time. Everybody in the world has to know about them, so that he can fight them—and then it may not be enough."

The viewpoint of the teleo sender changed as the two red beings soared away from their victims and angled slowly up the street. Peter reached out to switch off the scanner, and froze. The girl felt his muscles tense abruptly, looked back at the scene. The Invaders were floating up the sloping side of a tall, pure white structure that dominated the rest.

"That's the Atlas building," she said unbelievingly. "Us!"

"Yes."

Silently, they counted stories as the two beings rose. Forty-five ... forty-six ... forty-seven ... forty-eight. Inevitably, they halted. Then they faded slowly. It was impossible to say whether they had gone through the solid wall, or simply melted away.

The man and woman clung together, waiting.

There was a thick, oppressive silence, full of small rustlings and other faint sounds that were no longer normal. Then, very near, a man screamed in a high, inhuman voice. The screamed dwindled into a throaty gurgle and died, leaving silence again.

Peter's lips were cold with sweat. Tiny nerves in his face and arms were jumping convulsively. His stomach crawled. He thrust the girl away from him and started toward the inner room.

"Wait here," he mouthed.

She was after him, clinging to his arms. "No, Peter! Don't go in there! Peter!" But he pushed her away again, woodenly, and stalked forward.

There was a space in the middle of the room where machinery had been cleared away to make room for an incompleted setup. Peter walked down the narrow aisle, past bakelite-sheathed mechanisms and rows of animal cages, and paused just short of it.

The two red beings were there, formless bodies hazy in midair, the distorted, hairless skulls in profile, staring at something outside his range of vision.

Peter forced himself forward another step. Little Harry Kanin, Lorelei's assistant, was crumpled in a corner, half supported by the broad base of an X-ray chamber. His face was flaccid and bloated. His glazed eyes, impassive yet somehow pleading, stared at nothingness straight ahead of him.

The Invaders ignored Peter, staring expressionlessly down at Kanin. In a moment Peter realized what they were doing to him. He stood, paralyzed with horror, and watched it happen.

The little man's body was sagging, ever so slowly, as if he were relaxing tiredly. His torso was telescoping, bit by bit; his spread legs grew wider and more shapeless, his cheeks caved in and his skull grew gradually flatter.

When it was over, the thing that had been Kanin was a limp, boneless puddle of flesh. Peter could not look at it.

There was a scream in his throat that would not come out. He was beyond fear, beyond agony. He turned to the still-hovering monsters and said in a terrible voice, "Why? Why?"

The nearest being turned slowly to regard him. Its lips did not move, but there was a tiny sound in Peter's brain, a thin, dry whispering.

The scream was welling up. He fought it down and listened.

"Wurnkomellilonasendiktolsasangkanmiamiamimami...."

The face was staring directly into his, the bulging eyes hypnotic. The ears were small, no more than excresences of skin. The narrow lips seemed sealed together; a thin, slimy ichor drooled from them. There were lines in the face, but they were lines of age, not emotion. Only the eyes were alive.

"... raswilopreatadvuonistuwurncchtusanlgkelglawwalinom...."

"I can't understand," he cried wildly. "What do you want?"

"... morofelcovisyanmamiwurlectaunntous."

He heard a faint sound behind him, and whirled. It was the first time he had realized that Lorelei had followed him. She stood there, swaying, very pale, looking at the red Invaders. Her eyes swiveled slowly....

"Opreniktoulestritifenrelngetnaktwiltoctpre."

His voice was hoarse. "Don't look! Don't—Go back!" The horrible, mindless noise in his throat was almost beyond his power to repress. His insides writhed to thrust it out.

She didn't see him. Her eyes glazed, and she dropped limply to the floor.

The scream came out then. Before he knew, even, that he could hold it back no longer, his mouth was wide open, his muscles tensed, his fingernails slicing his palms. It echoed with unbelievable volume in the room. It was a scream to split eardrums; a scream to wake the dead.

Somebody said, "Doctor!"

He wanted to say, "Yes, get a doctor. Lorelei—" but his mouth only twitched feebly. He couldn't seem to get it to work properly.

He tried again. "Doctor."

"Yes?" A gentle, masculine voice.

He opened his eyes with an effort. There was a blurred face before him; in a moment it grew clearer. The strong, clean-shaven chin contrasted oddly with the haggard circles under the eyes. There was a clean, starched odor.

"Where am I?" he said. He tried to turn his head, but a firm hand pressed him back into the sheets.

"You're in a hospital. Just lie quietly, please."

He tried to get up again. "Where's Lorelei?"

"She's well, and you'll see her soon. Now lie quietly. You've been a very sick man."

Peter sank back in the bed. The room was coming into focus. He looked around him slowly. He felt very weak, but perfectly lucid.

"Yes...." he said. "How long have I been here, Doctor?"

The man hesitated, looked at him intently. "Three months," he said. He turned and gave low-voiced instructions to a nurse, and then went away.

Peter's head began spinning just a little. Glass clinked from a metal stand near his head; the nurse bent over him with a glass half full of milky fluid. It tasted awful, but she made him drink it all.

In a moment he began to relax, and the room got fuzzy again. Just before he drifted off, he said sleepily, "You can't—fool me. It's been more—than three—months."

He was right. All the nurses, and even Dr. Arnold, were evasive, but he kept asking them why he couldn't see Lorelei, and finally he wormed it out of them. It had been nine and a half months, not three, and he'd been in a coma all that time. Lorelei, it seemed, had recovered much sooner.

"She was only suffering from ordinary shock," Arnold explained. "Seeing that assistant of hers—it was enough to knock anybody out, especially a woman. But you stood actual mental contact with them for approximately five minutes. Yes, we know—you talked a lot. It's a miracle you're alive, and rational."

"But where is she?" Peter complained. "You still haven't explained why I haven't been able to see her."

Arnold frowned. "All right," he said. "I guess you're strong enough to take it. She's underground, with the rest of the women and children, and a good two-thirds of the male population. That's where you'll go, as soon as you're well enough to be moved. We started digging in six months ago."

"But why?" Peter whispered.

Arnold's strong jaw knotted. "We're hiding," he said. "Everything else has failed."

Peter couldn't think of anything to say. Dr. Arnold's voice went on after a moment, musingly. "We're burrowing into the earth, like worms. It didn't take us long to find out we couldn't kill them. They didn't even take any notice of our attempts to do so, except once. That was when a squadron of the Police caught about fifty of them together at one time, and attacked with flame guns and a new secret weapon. It didn't hurt them, but it annoyed them. It was the first time they'd been annoyed, I think. They blew up half a state, and it's still smoldering."

"And since then?" Peter asked huskily.

"Since then, we've been burrowing. All the big cities.... It would be an impossible task if we tried to include all the thinly-populated areas, of course, but it doesn't matter. By the time we excavate enough to take care of a quarter of the earth's population, the other three-quarters will be dead, or worse."

"I wonder," Peter said shakily, "if I am strong enough to take it."

Arnold laughed harshly. "You are. You've got to be. You're part of our last hope, you see."

"Our last hope?"

"Yes. You're a scientist."

"I see," said Peter. And for the first time, he thought of the Citadel. No plan leaped full-born into his mind, but, maybe, he thought, there's a chance....

It wasn't very big, the thing that had been his shining dream. It lay there in its rough cradle, a globe of raw dura-steel not more than five hundred meters in diameter, where the Citadel was to have been a thousand. It wouldn't house a hundred scientists, eagerly delving into the hinterland of research. The huge compartments weren't filled with the latest equipment for chemical and physical experiment; instead, there was compressed oxygen there, and concentrated food, enough to last a lifetime.

It was a new world, all by itself; or else it was a tomb. And there was one other change, one that you couldn't see from the outside. The solid meters of lead in its outer skin, the shielding to keep out cosmic rays, were gone.

A man had just finished engraving the final stroke on its nameplate, to the left of the airlock—The Avenger. He stepped away now, and joined the group a little distance away, silently waiting.

Lorelei said, "You can't do it. I won't let you! Peter—"

"Darling," he began wearily.

"Don't throw your life away! Give us time—there must be another way."

"There's no other way," Peter said. He gripped her arms tightly, as if he could compel her to understand by the sheer pressure of his fingers. "Darling, listen to me. We've tried everything. We've gone underground, but that's only delaying the end. They still come down here, only not as many. The mortality rate is up, the suicide rate is up, the birth rate is down, in spite of anything we can do. You've seen the figures: we're riding a curve that ends in extinction fifty years from now.

"They'll live, and we'll die, because they're a superior race. We're a million years too far back even to understand what they are or where they came from. Besides them, we're apes. There's only one answer."

She was crying now, silently, with great racking sobs that shook her slender body. But he went remorselessly on.

"Out there, in space, the cosmics change unshielded life. They make tentacles out of arms; or scales out of hair; or twelve toes, or a dozen ears—or a better brain. Out of those millions of possible mutations, there's one that will save the human race. We can't fight them, but a superman could. That's our only chance. Lorelei—darling—don't you see that?"

She choked, "But why can't you take me along?"

He stared unseeingly past her wet, upturned face. "You know why," he said bitterly. "Those rays are strong. They don't only work on embryos; they change adult life forms, too. I have one chance in seven of staying alive. You'd have one chance in a million of staying beautiful. I couldn't stand that. I'd kill myself, and then humanity would die, too. You'd be their murderer."

Her sobs gradually died away. She straightened slowly until he no longer had to support her, but all the vitality and resilience was gone out of her body. "All right," she said in a lifeless voice. "You'll come back, Peter."

He turned away suddenly, not trusting himself to kiss her goodbye. A line from an old film kept echoing through his head. "They'll come back—but not as boys!"

We'll come back, but not as men.

We'll come back, but not as elephants.

We'll come back, but not as octopi.

He was trembling violently. He ran the last few steps, stumbled into the airlock, and pressed the stud that would seal the door behind him. We'll come back.... He heard the massive disk sink home, closing him off. Then he sank down on the floor of the airlock and put his head in shaking hands.

After a while he roused himself, closed the inner door of the lock behind him, and walked down the long corridor into the control chamber. The shining banks of keys were there, waiting for his touch; he slumped down before them and listlessly closed the contact of the visiplate.

He swung its field slowly, scanning for the last time the bare walls of the underground chamber, making sure that all the spectators had retired out of the way of the blast. Then his clawed fingers poised over the keys, hovered a moment, and thrust down.

Acceleration pressed him deep into his chair. In the visiplate, the heavy doors that closed the tunnel above him flashed back, one by one. The energy-charged screen flickered off to let him pass, and closed smoothly behind him. The last doors, cleverly camouflaged, slipped back into place and then dwindled in the distance. It was done.

He flashed on out, past the moon, past Mars, over the asteroid belt. The days merged into weeks, then months, and finally, far out, The Avenger curved into an orbit and held it. The great motors died, and the silence pressed in about him.

Already he could feel the invisible rays burning resistlessly through his flesh as if it were water, shifting the cells of his body, working its slow, monstrous alchemy upon him. Peter waited until the changes were unmistakably evident in his skin and hair, and then he smashed all the mirrors in the ship.

The embryos were pulsing with unnatural life, even in the suspended animation of their crystal cells. One by one he allowed them to mature, and after weeks or years destroyed the monstrosities that came from the incubators. Time went by, meaninglessly. He ate when he was hungry, slept when his driving purpose let him, and worked unceasingly, searching for the million-to-one chance.

He stared sometimes through changed eyes at the tiny blue star that was Earth, wondering if the race he had left behind still burrowed in its worm-tunnels, digging deeper and deeper away from the sunlight. But after a time he ceased even to wonder.

And one changeling-child he did not destroy. He fed knowledge to its eager brain, and watched it through the swift years, with a dawning hope....

Peter closed the diary. "The rest you know, Robert," he said.

"Yes," I told him. "I was that child. I am the millionth mutation you were searching for."

His eyes glowed suddenly in their misshapen sockets. "You are. Your brain is as superior to mine as mine is to an anthropoid's. You solve instinctively problems that would take our mechanical computers hours of work. You are a superman."

"I am without your imperfections," I said, flexing my arms.

He rose and strode nervously over to the window. I watched him as he stood there, outlined against the blazing galaxies. He had changed but little in the years that I had known him. His lank gray hair straggled over his sunken eyes; his cheeks were blobbed with excresences of flesh; one corner of his mouth was drawn up in a perpetual grin. He had a tiny sixth finger on his left hand.

He turned again, and I saw the old scar on his cheek where I had once accidentally drawn one of my talons across his face.

"And now," he said softly, "we will go home. I've waited so long—keeping the control chamber and the engine room locked away from you, not telling you, even, about Earth until now—because I had to be sure. But now, the waiting is over.

"They're still there, I'm sure of it—the people, and the Invaders. You can kill the Invaders, Robert."

He looked at me, a little oddly, almost as if he had some instinctive knowledge of what was to come. But he went on swiftly, "On Earth we had a saying: 'Fight fire with fire.' That is the way it will be with you. You are completely, coldly logical, just as they are. You can understand them, and so you can conquer them."

I said, "That is the reason why we will not go back to Earth."

He stared at me, his jaw slack, his hands trembling. "What—what did you say?"

I repeated it patiently.

"But why?" he cried, sinking down into the chair before me. In an instant all the joy had gone out of him. I could not understand his suffering, but I could recognize it.

"You yourself have said it," I told him. "I am a being of logic, just as the beings who have invaded your planet are. I do not comprehend the things which you call hate, fear, joy and love, as they do not. If I went to Earth, I would use your people to further my knowledge, just as the invaders do. I would have no reason to kill the invaders. They are more nearly kin to me than your people."

Peter's eyes were dull, his limbs slumped. For a moment I thought that the shock had deranged his mind.

His voice trembled when he said, "But if I ask you to kill them, and not my people?"

"To do so would be illogical."

He waved his hands helplessly. "Gratitude?" he muttered.

"No, you don't understand that, either."

Then he cried suddenly, "But I am your friend, Robert!"

"I do not understand 'friend,'" I said.

I did understand "gratitude," a little. It was a reciprocal arrangement: I did what Peter wished, so long as I did not actively want to do otherwise, because he had done things for me. Very well, then we must not go back. It was very simple, but I knew that he could not comprehend it.

I tried to explain it to him, however. But he only stared at me, with an expression on his face that I had never seen there before, and that, somehow, I did not like to see. It was disquieting, and so I hastened to the end that I knew was inevitable.

"Will you promise," I asked, "to abide by my decision?"

He kept on looking at me, his lips trembling in their fixed grin. "No!" he said. "Never! You'll change your mind some day—you must! We'll go back, then—I'll make you go back! Lorelei—" He collapsed, sobbing, his head sunk in his arms.

I knew that what he said was partly true. Some day, when I slept, as I would have to within months, he would go down to the control room, set the keys for the return, and lock the combinations of the doors behind him again. Sooner or later, in spite of me, The Avenger would go home. There was only one thing to do.

He was still slumped in his chair, his body shaken by his sobs. I rose silently, and stood for a moment looking down at him. It was best that it happen now; it was what he would have called "mercy."

I extended my arms, looking at the corded, black-furred length of them. I looked down at him once more, saying a silent farewell; and then I clasped his gray head, very quickly, between my hands.