Andrew Harlan watched the men at work with abstracted eyes. They ignored him politely because he was a Technician. Ordinarily he would have ignored them somewhat less politely because they were Maintenance men. But now he watched them and, in his misery, he even caught himself envying them.

They were service personnel from the Department of Intertemporal Transportation, in dun-gray uniforms with shoulder patches showing a red, double-headed arrow against a black background. They used intricate force-field equipment to test the kettle motors and the degrees of hyper-freedom along the kettleways. They had, Harlan imagined, little theoretical knowledge of temporal engineering, but it was obvious that they had a vast practical knowledge of the subject.

Harlan had not learned much concerning Maintenance when he was a Cub. Or, to put it more accurately, he had not really wished to learn. Cubs who did not make the grade were put into Maintenance. The "unspecialized profession" (as the euphemism had it) was the hallmark of failure and the average Cub automatically avoided the subject.

Yet now, as he watched the Maintenance men at work, they seemed to Harlan to be quietly, tensionlessly efficient, reasonably happy.

Why not? They outnumbered the Specialists, the "true Eternals," ten to one. They had a society of their own, residential levels devoted to them, pleasures of their own. Their labor was fixed at so many hours per physioday and there was no social pressure in their case to make them relate their spare-time activity to their profession. They had time, as Specialists did not, to devote to the literature and film dramatizations culled out of the various Realities.

It was they, after all, who probably had the better-rounded personalities. It was the Specialist's life which was harried and affected, artificial in comparison with the sweet and simple life in Maintenance.

Maintenance was the foundation of Eternity. Strange that such an obvious fact had not struck him earlier. They supervised the importation of food and water from Time, the disposal of waste, the functioning of the power plants. They kept all the machinery of Eternity running smoothly. If every Specialist were to die of a stroke on the spot, Maintenance could keep Eternity going indefinitely. Yet were Maintenance to disappear, the Specialists would have to abandon Eternity in days or die miserably.

Did Maintenance men resent the loss of their homewhens, or their womanless, childless lives? Was security from poverty, disease, and Reality Change sufficient compensation? Were their views ever consuited on any matter of importance? Harlan felt some of the fire of the social reformer within him.

Senior Computer Twissell broke Harlan's train of thought by bustling in at a half run, looking even more haunted than he had an hour before, when he had left, with Maintenance already at work.

Harlan thought: How does he keep it up? He's an old man.

Twissell glanced about him with birdlike brightness as the men automatically straightened up to respectful attention.

He said, "What about the kettleways?"

One of the men responded, "Nothing wrong, sir. The ways are clear, the fields mesh."

"You've checked everything?"

"Yes, sir. As far upwhen as the Department's stations go."

Twissell said, "Then go."

There was no mistaking the brusque insistence of his dismissal. They bowed respectfully, turned, and hastened out briskly.

Twissell and Harlan were alone in the kettleways.

Twissell turned to him. "You'll stay here. Please."

Harlan shook his head. "I must go."

Twissell said, "Surely you understand. If anything happens to me, you still know how to find Cooper. If anything happens to you, what can I or any Eternal or any combination of Eternals do alone?"

Harlan shook his head again.

Twissell put a cigarette between his lips. He said, "Sennor is suspicious. He's called me several times in the last two physiodays. Why am I in seclusion, he wants to know. When he finds out I've ordered a complete overhaul of the kettleway machinery... I must go now, Harlan. I can't delay."

"I don't want delay. I'm ready."

"You insist on going?"

"If there's no barrier, there'll be no danger. Even if there is, I've been there already and come back. What are you afraid of, Computer?"

"I don't want to risk anything I don't have to."

"Then use your logic, Computer. Make the decision that I'm to go with you. If Eternity still exists after that, then it means that the circle can still be closed. It means we'll survive. If it's a wrong decision, then Eternity will pass into nonexistence, but it will anyway if I don't go, because without Noys, I'll make no move to get Cooper. I swear it."

Twissell said, "I'll bring her back to you."

"If it is so simple and safe, there will be no harm if I come along."

Twissell was in an obvious torture of hesitation. He said gruffly, "Well, then, come!"

And Eternity survived.

Twissell's haunted look did not disappear once they were within the kettle. He stared at the skimming figures of the temporometer. Even the scaler gauge, which measured in units of Kilocenturies, and which the men had adjusted for this particular purpose, was clicking at minute intervals.

He said, "You should not have come."

Harlan shrugged. "Why not?"

"It disturbs me. No sensible reason. Call it a long-standing superstition of mine. It makes me restless." He clasped his hands together, holding them tightly.

Harlan said, "I don't understand you."

Twissell seemed eager to talk, as though to exorcise some mental demon. He said, "Maybe you'll appreciate this, at that. You're the expert on the Primitive. How long did man exist in the Primitive?"

Harlan said, "Ten thousand Centuries. Fifteen thousand, maybe."

"Yes. Beginning as a kind of primitive apelike creature and ending as Homo sapiens. Right?"

"It's common knowledge. Yes."

"Then it must be common knowledge that evolution proceeds at a fairly rapid pace. Fifteen thousand Centuries from ape to Homo sapiens."

"Well?"

"Well, I'm from a Century in the 30,000's--"

(Harlan could not help starting. He had never known Twissell's homewhen or known of anyone who did.)

"I'm from a Century in the 30,000's," Twissell said again, "and you're from the 95th. The time between our homewhens is twice the total length of time of man's existence in the Primitive, yet what change is there between us? I was born with four fewer teeth than you, and without an appendix. The physiological differences about end with that. Our metabolism is almost the same. The major difference is that your body can synthesize the steroid nucleus and my body can't, so that I require cholesterol in my diet and you don't. I was able to breed with a woman of the 575th. That's how undifferentiated with time the species is."

Harlan was unimpressed. He had never questioned the basic identity of man throughout the Centuries. It was one of those things you lived with and took for granted. He said, "There have been cases of species living unchanged through millions of Centuries."

"Not many, though. And it remains a fact that the cessation of human evolution seems to coincide with the development of Eternity. Just coincidence? It's not a question which is considered, except by a few here and there like Sennor, and I've never been a Serinor. I didn't believe speculation was proper. If something couldn't be checked by a Computaplex, it had no business taking up the time of a Computer. And yet, in my younger days, I sometimes thought--"

"Of what?" Harlan thought: Well, it's something to listen to, anyway.

"I sometimes thought about Eternity as it was when it was first established. It stretched over just a few Centuries in the 30's and 40's, and its function was mostly trade. It interested itself in the ref orestation of denuded areas, shipping topsoil back and forth, fresh water, fine chemicals. Those were simple days.

"But then we discovered Reality Changes. Senior Computer Henry Wadsman, in the dramatic manner with which we are all acquainted, prevented a war by removing the safety brake of a Congressman's ground vehicle. After that, more and more, Eternity shifted its center of gravity from trade to Reality Change. Why?"

Harlan said, "The obvious reason. Betterment of humanity."

"Yes. Yes. In normal times, I think so too. But I'm talking of my nightmare. What if there were another reason, an unexpressed one, an unconscious one. A man who can travel into the indefinite future may meet men as far advanced over himself as he himself is over an ape. Why not?"

"Maybe. But men are men--"

"-even in the 70,000th. Yes, I know. And have our Reality Changes had something to do with it? We bred out the unusual. Even Sennor's homewhen with its hairless creatures is under continual question and that's harmless enough. Perhaps in all honesty, in all sincerity, we've prevented human evolution because we don't want to meet the supermen."

Still no spark was struck. Harlan said, "Then it's done. \Vhat does it matter?"

"But what if the superman exists just the same, further upwhen than we can reach? We control only to the 70,000th. Beyond that are the Hidden Centuries! Why are they hidden? Because evolved man does not want to deal with us and bars us from his time? Why do we allow them to remain hidden? Because we don't want to deal with them and, having failed to enter in our first attempt, we refuse even to make additional attempts? I don't say it's our conscious reason, but conscious or unconscious, it's a reason."

"Grant everything," said Harlan sullenly. "They're out of our reach and we're out of theirs. Live and let live."

Twissell seemed struck by the phrase. "Live and let live. But we don't. We make Changes. The Changes extend only through a few Centuries before temporal inertia causes its effects to die out. You remember Sennor brought that up as one of the unanswered problems of Time at our breakfast. What he might have said was that it's all a matter of statistics. Some Changes affect more Centuries than other. Theoretically, any number of Centuries can be affected by the proper Change; a hundred Centuries, a thousand, a hundred thousand. Evolved man of the Hidden Centuries may know that. Suppose he is disturbed by the possibility that someday a Change may reach him clear to the 200,000th."

"It's useless to worry about such things," said Harlan with the air of a man who had much greater worries.

"But suppose," went on Twissell in a whisper, "they were calm enough as long as we left the Sections of the Hidden Centuries empty. It meant we weren't aggressing. Suppose this truce, or whatever you wish to call it, were broken, and someone appeared to have established permanent residence upwhen from the 70,000th. Suppose they thought it might mean the first of a serious invasion? They can bar us from their Time, so their science is that far advanced beyond ours. Suppose they may further do what seems impossible to us and throw a barrier across the kettleways, cutting us off--"

And now Harlan was on his feet, in full horror, "They have Noys?"

"I don't know. It's speculation. Maybe there is no barrier. Maybe there was something wrong with your ket-"

"There was a barrier!" yelled Harlan. "What other explanation is there? Why didn't you tell me this before."

"I didn't believe it," groaned Twissell. "I still don't. I shouldn't have said a word of this foolish dreaming. My own fears-the question of Cooper-everything- But wait, just a few minutes."

He pointed at the temporometer. The scaler indicated them to be between the 95,000th and 96,000th Centuries.

Twissell's hand on the controls slowed the kettle. The 99,000th was passed. The scaler's motions stopped. The individual Centuries could be read.

99,726-99,727-99,728- "What will we do?" muttered Harlan.

Twissell shook his head in a gesture that spoke eloquently of patience and hope, but perhaps also of helplessness.

99,851-99,852-99,853- Harlan steeled himself for the shock of the barrier and thought desperately: Would preserving Eternity be the only means of finding time to fight back at the creatures of the Hidden Centuries? How else recover Noys? Dash back, back to the 575th and work like fury to- 99,938-99,939-99,940- Harlan held his breath. Twissell slowed the kettle further, let it creep. It responded perfectly to the controls.

99,984-99,985-99,986- "Now, now, now," said Harlan in a whisper, unaware that he had made any sound at all.

99,998-99,999-100,000-100,001-100,002- The numbers mounted and the two men watched them continue to mount in paralytic silence.

Then Twissell cried, "There is no barrier."

And Harlan answered, "There was! There was!" Then, in agony, "Maybe they've got her, and need a barrier no longer."

111,394th!

Harlan leaped from the kettle, and raised his voice. "Noys! Noys!"

The echoes bounced off the walls of the empty Section in hollow syncopation.

Twissell, climbing out more sedately, called after the younger man, "Wait, Harlan--"

That was useless. Harlan, at a run, was hurtling along the corridors toward that portion of the Section they had made a kind of home.

He thought vaguely of the possibility of meeting one of Twissell's "evolved men" and momentarily his skin prickled, but then that was drowned in his urgent need to find Noys.

"Noys!"

And all at once, so quickly that she was in his arms before he was sure he had seen her at all, she was there and with him, and her arms were around him and clutching him and her cheek was against his shoulder and her dark hair was soft against his chin.

"Andrew?" she said, her voice muffled by the pressure of his body. "Where were you? It's been days and I was getting frightened."

Harlan held her out at arm's length, staring at her with a kind of hungry solemnity. "Are you all right?"

"I'm all right. I thought something might have happened to you. I thought--" She broke off, terror springing into her eyes and gasped, "Andrew!"

Harlan whirled.

It was only Twissell, panting.

Noys must have gained confidence from Harlan's expression. She said more quietly, "Do you know him, Andrew? Is it all right?"

Harlan said, "It's all right. This is my superior, Senior Computer Laban Twissell. He knows of you."

"A Senior Computer?" Noys shrank away.

Twissell advanced slowly. "I will help you, my child. I will help you both. The Technician has my promise, if he would only believe it."

"My apologies, Computer," said Harlan stiffly, and not yet entirely repentant.

"Forgiven," said Twissell. He held out his hand, took the girl's reluctant one. "Tell me, girl, has it been well with you here?"

"I've been worried."

"There's been no one here, since Harlan last left you."

"N-no, sir."

"No one at all? Nothing?"

She shook her head. Her dark eyes sought Harlan's. "Why do you ask?"

"Nothing, girl. A foolish nightmare. Come, we will take you back to the 575th."

On the kettle back Andrew Harlan sank, by degrees, into a troubled and deepening silence. He did not look up when the 100,000th was passed in the downwhen direction and Twissell had snorted an obvious sigh of relief as though he had half expected to be trapped on the upwhen side.

He scarcely moved when Noys's hand stole into his, and the manner in which he returned the pressure of her fingers was almost mechanical.

Noys slept in another room and now Twissell's restlessness reached a peak of devouring intensity.

"The advertisement, boy! You have your woman. My part of the agreement is done."

Silently, still abstracted, Harlan turned the pages of the volume on the desk. He found his page.

"It's simple enough," he said, "but it's in English. I'll read it to you and then translate it."

It was a small advertisement in the upper left-hand corner of a page numbered 30. Against an irregular line drawing as background were the unadorned words, in block letters:

ALL THE TALK OF THE MARKET

Underneath, in smaller letters, it said; "Investments News-Letter, P.O. Box 14, Denver, Colorado."

Twissell listened painstakingly to Harlan's translation and was obviously disappointed. He said, "What is the market? What do they mean by that?"

"The stock market," said Harlan impatiently. "A system by which private capital was invested in business. But that's not the point at all. Don't you see the line drawing against which the advertisement is set?"

"Yes. The mushroom cloud of an A-bomb blast. An attention getter. What about it?"

Harlan exploded. "Great Time, Computer, what's wrong with you? Look at the date of the magazine issue."

He pointed to the top heading, just to the left of the page number. It read March 28, 1932.

Harlan said, "That scarcely needs translation. The numbers are about those of Standard Intertemporal and you see it's the 19.32nd Century. Don't you know that at that time no human being who had ever lived had seen the mushroom cloud? No one could possibly reproduce it so accurately, except--"

"Now, wait. It's just a line pattern," said Twissell, trying to retain his equilibrium. "It might resemble the mushroom cloud only coincidentally."

"Might it? Will you look at the wording again?" Harlan's fingers punched out the short lines: "All the-Talk-Of the-Market. The initials spell out ATOM, which is English for atom. Is that coincidence, too? Not a chance.

"Don't you see, Computer, how this advertisement fits the conditions you yourself set up? It caught my eye instantly. Cooper knew it would out of sheer anachronism. At the same time, it has no meaning other than its face value, no meaning at all, for any man of the 19.32nd.

"So it must be Cooper. That's his message. We have the date to the nearest week of a Centicentury. We have his mailing address. It is only necessary to go after him and I'm the only one with enough knowledge of the Primitive to manage that."

"And you'll go?" Twissell's face was ablaze with relief and happiness.

"I'll go-on one condition."

Twissell frowned in a sudden reversal of emotion. "Again conditions?"

"The same condition. I'm not adding new ones. Noys must be safe. She must come with me. I will not leave her behind."

"You still don't trust me? In what way have I failed you? What can there be that still disturbs you?"

"One thing, Computer," said Harlan solemnly. "One thing still. There was a barrier across the 100,000th. Why? That is what still disturbs me."