It was with a dull surprise that Technician Andrew Harlan, on bursting into the 575th, found himself in the night shift. The passing of the physiohours had gone unnoticed during his wild streaks along the kettle shafts. He stared hollowly at the dimmed corridors, the occasional evidence of the thinned-out night force at work.

But in the continued grip of his rage Harlan did not pause long to watch uselessly. He turned toward personal quarters. He would find Twissell's room on Computer Level as he had found Finge's and he had as little fear of being noticed or stopped.

The neuronic whip was still hard against his elbow as he stopped before Twissell's door (the name plate upon it advertising the fact in clear, inlaid lettering).

Harlan activated the door signal brashly on the buzzer level. He shorted the contact with a damp palm and let the sound become continuous. He could hear it dimly.

A step sounded lightly behind him and he ignored it in the sure knowledge that the man, whoever he was, would ignore him. (Oh, rose-red Technician's patch!)

But the sound of steps halted and a voice said, "Technician Harlan?"

Harlan whirled. It was a Junior Computer, relatively new to the Section. Harlan raged inwardly. This was not quite the 482nd. Here he was not merely a Technician, he was Twissell's Technician, and the younger Computers, in their anxiety to ingratiate themselves with the great Twissell, would extend a minimum civility to his Technician.

The Computer said, "Do you wish to see Senior Computer Twissell?"

Harlan fidgeted and said, "Yes, sir." (The fool! What did he think anyone would be standing signaling at a man's door for? To catch a kettle?)

"I'm afraid you can't," said the Computer.

"This is important enough to wake him," said Harlan.

"Maybe so," said the other, "but he's outwhen. He's not in the 575th."

"Exactly when is he, then?" asked Harlan impatiently.

The Computer's glance became a supercilious stare. "I wouldn't know."

Harlan said, "But I have an important appointment first thing in the morning."

"You have," said the Computer, and Harlan was at a loss to account for his obvious amusement at the thought.

The Computer went on, even smiling now, "You're a little early, aren't you?"

"But I must see him."

"I'm sure he'll be here in the morning." The smile broadened.

"But--"

The Computer passed by Harlan, carefully avoiding any contact, even of garments.

Harlan's fists clenched and unclenched. He stared helplessly after the Computer and then, simply because there was nothing else to do, he walked slowly, and without full consciousness of his surroundings, back to his own room.

Harlan slept fitfully. He told himself he needed sleep. He tried to relax by main force, and, of course, failed. His sleep period was a succession of futile thought.

First of all, there was Noys.

They would not dare harm her, he thought feverishly. They could not send her back to Time without first calculating the effect on Reality and that would take days, probably weeks. As an alternative, they might do to her what Finge had threatened for him; place her in the path of an untraceable accident.

He did not take that into serious consideration. There was no necessity for drastic action such as that. They would not risk Harlan's displeasure by doing it. (In the quiet of a darkened sleeping room, and in that phase of half sleep where things often grew queerly disproportionate in thought, Harlan found nothing grotesque in his sure opinion that the Allwhen Council would not dare risk a Technician's displeasure.)

Of course, there were uses to which a woman in captivity might be put. A beautiful wOman from a hedonistic Reality.

Resolutely Harlan put the thought away as often as it returned. It was at once more likely and more unthinkable than death, and he would have none of it.

He thought of Twis sell.

The old man was out of the 575th. Where was he during hours when he should have been asleep? An old man needs his sleep. Harlan was sure of the answer. There were Council consultations going on. About Harlan. About Noys. About what to do with an indispensable Technician one dared not touch.

Harlan's lips drew back. If Finge reported Harlan's assault of that evening, it would not affect their considerations in the least. His crimes could scarcely be worsened by it. His indispensability would certainly not be lessened.

And Harlan was by no means certain that Finge would report him. To admit having been forced to cringe before a Technician would put an Assistant Computer in a ridiculous light, and Finge might not choose to do so.

Harlan thought of Technicians as a group, which, of late, he had done rarely. His own somewhat anomalous position as Twissell's man and as half an Educator had kept him too far apart from other Technicians. But Technicians lacked solidarity anyway. Why should that be?

Did he have to go through the 575th and the 482nd rarely seeing or speaking to another Technician? Did they have to avoid even one another? Did they have to act as though they accepted the status into which the superstition of others forced them?

In his mind he had already forced the capitulation of the Council as far as Noys was concerned, and now he was making further demands. The Technicians were to be allowed an organization of their own, regular meetings-more friendship-better treatment from the others.

His final thought of himself was as a heroic social revolutionary, with Noys at his side, when he sank finally into a dreamless sleep..

The door signal awoke him. It whispered at him with hoarse impatience. He collected his thoughts to the point of being able to look at the small clock beside his bed and groaned inwardly.

Father Time! After all that he had overslept.

He managed to reach the proper button from bed and the viewsquare high on the door grew transparent. He did not recognize the face, but it carried authority whoever it was.

He opened the door and the man, wearing the orange patch of Administration, stepped in.

"Technician Andrew Harlan?"

"Yes, Administrator? You have business with me?"

The Administrator seemed in no wise discommoded at the sharp belligerence of the question. He said, "You have an appointment with Senior Computer Twissell?"

"Well?"

"I am here to inform you that you are late."

Harlan stared at him. "What's this all about? You're not from the 575th, are you?"

"The 222nd is my station," said the other frigidly. "Assistant Administrator Arbut Lemm. I'm in charge of the arrangements and I'm trying to avoid undue excitement by by-passing official notification over the Communiplate."

"What arrangements? What excitement? What's it all about? Listen, I've had conferences with Twissell before. He's my superior. There's no excitement involved."

A look of surprise passed momentarily over the studious lack of expression the Administrator had so far kept on his face. "You haven't been informed?"

"About what?"

"Why, that a subcommittee of the Allwhen Council is holding session here at the 575th. This place, I am told, has been alive with the news for hours."

"And they want to see me?" As soon as he asked that, Harlan thought: Of course they want to see me. What else could the session be about but me?

And he understood the amusement of the Junior Computer last night outside Twissell's room. The Computer knew of the projected committee meeting and it amused him to think that a Technician could possibly expect to see Twissell at a time like that. Very amusing, thought Harlan bitterly.

The Administrator said, "I have my orders. I know nothing more." Then, still surprised, "You've heard nothing of this?"

"Technicians," said Harlan sarcastically, "lead sheltered lives."

Five besides Twissell! Senior Computers all, none less than thirtyfive years an Eternal.

Six weeks earlier Harlan would have been overwhelmed by the honor of sitting at lunch with such a group, tongue-tied by the combination of responsibility and power they represented. They would have seemed twice life-size to him.

But now they were antagonists of his, worse still, judges. He had no time to be impressed. He had to plan his strategy.

They might not know that he was aware they had Noys. They could not know unless Finge told them of his last meeting with Harlan. In the clear light of day, however, he was more than ever convinced that Finge was not the man to broadcast publicly the fact that he had been browbeaten and insulted by a Technician.

It seemed advisable, then, for Harlan to nurse this possible advantage for the time being, to let them make the first move, say the first sentence that would join actual combat.

They seemed in no hurry. They stared at him placidly over an abstemious lunch as though he were an interesting specimen spreadeagled against a plane of force by mild repulsors. In desperation Harlan stared back.

He knew all of them by reputation and by trimensional reproduction in the physiomonthly orientation films. The films co-ordinated developments throughout the various Sections of Eternity and were required viewing for all Eternals with rating from Observer up.

August Sennor, the bald one (not even eyebrows or eyelashes), of course attracted Harlan most. First, because the odd appearance of those dark, staring eyes against bare eyelids and forehead was remarkably greater in person than it had ever seemed in trimension. Second, because of his knowledge of past collisions of view between Sennor and Twissell. Finally, because Sennor did not confine himself to watching Harlan. He shot questions at him in a sharp voice.

For the most part his questions were unanswerable, such as: "How did you first come to be interested in Primitive times, young man?" "Do you find the study rewarding, young man?"

Finally, he seemed to settle himself in his seat. He pushed his plate casually onto the disposal chute and clasped his thick fingers lightly before him. (There was no hair on the back of the hands, Harlan noticed.)

Sennor said, "There is something I have always wanted to know. Perhaps you can help me."

Harlan thought: All right, now, this is it.

Aloud he said, "If I can, sir."

"Some of us here in Eternity-I won't say all, or even enough" (and he cast a quick glance at Twissell's tired face, while the others drew closer to listen) "but some, at any rate-are interested in the philosophy of Time. Perhaps you know what I mean."

"The paradoxes of Time-travel, sir?"

"Well, if you want to put it melodramatically, yes. But that's not all, of course. There is the question of the true nature of Reality, the question of the conservation of mass-energy during Reality Change and so on. Now we in Eternity are influenced in our consideration of such things by knowing the facts of Time-travel. Your creatures of the Primitive era, however, knew nothing of Time-travel. What were their views on the matter?"

Twissell's whisper carried the length of the table. "Cobwebs!"

But Sennor ignored that. He said, "Would you answer my question, Technician?"

Harlan said, "The Primitives gave virtually no thought to Timetravel, Computer."

"Did not consider it possible, eh?"

"I believethat's right."

"Did not even speculate?"

"Well, as to that," said Harlan uncertainly, "I believe there were speculations of sorts in some types of escape literature. I am not well acquainted with these, but I believe a recurrent theme was that of the man who returned in Time to kill his own grandfather as a child."

Sennor seemed delighted. "Wonderful! Wonderful! After all, that is at least an expression of the basic paradox of Time-travel, if we assume an indeviant Reality, eh? Now your Primitives, I'll venture to state, never assumed anything but an indeviant Reality. Am I right?"

Harlan waited to answer. He did not see where the conversation was aiming or what Sennor's deeper purposes were, and it unnerved him. He said, "I don't know enough to answer you with certainty, sir. I believe there may have been speculations as to alternate paths of time or planes of existence. I don't know."

Sennor thrust out a lower lip. "I'm sure you're wrong. You may have been misled by reading your own knowledge into various ambiguities you may have come across. No, without actual experience of Time-travel, the philosophic intricacies of Reality would be quite beyond the human mind. For instance, why does Reality possess inertia? We all know that it does. Any alteration in its flow must reach a certain magnitude before a Change, a true Change, is effected. Even then, Reality has a tendency to flow back to its original position.

"For instance, suppose a Change here in the 575th. Reality will change with increasing effects to perhaps the 600th. It will change, but with continually lesser effects to perhaps the 650th. Thereafter, Reality will be unchanged. We all know this is so, but do any of us know why it is so? Intuitive reasoning would suggest that any Reality Change would increase its effects without limit as the Centuries pass, yet that is not so.

"Take another point. Technician Harlan, I'm told, is excellent at selecting the exact Minimum Change Required for any situation. I'll wager he cannot explain how he arrives at his own choice.

"Consider how helpless the Primitives must be. They worry about a man killing his own grandfather because they do not understand the truth about Reality. Take a more likely and a more easily analyzed case and let's consider the man who in his travels through time meets himself--"

Harlan said sharply, "What about a man who meets himself?"

The fact that Harlan interrupted a Computer was a breach of manners in itself. His tone of voice worsened the breach to a scandalous extent, and all eyes turned reproachfully on the Technician.

Sennor harumphed, but spoke in the strained tone of one determined to be polite despite nearly insuperable difficulties. He said, continuing his broken sentence and thus avoiding the appearance of answering directly the unmannerly question addressed to him, "And the four subdivisions into which such an act can fall. Call the man earlier in physiotime, A, and the one later, B. Subdivision one, A and B may not see one another, or do anything that will significantly affect one another. In that case, they have not really met and we may dismiss this case as trivial.

"Or B, the later individual, may see A while A does not see B. Here, too, no serious consequences need be expected. B, seeing A, sees him in a position and engaged in activity of which he already has knowledge. Nothing new is involved.

"The third and fourth possibilities are that A sees B, while B does not see A, and that A and B see one another. In each possibility, the serious point is that A has seen B; the man at an earlier stage in his physiological existence sees himself at a later stage. Observe that he has learned he will be alive at the apparent age of B. He knows he will live long enough to perform the action he has witnessed. Now a man in knowing his own future in even the slightest detail can act on that knowledge and therefore changes his future. It follows that Reality must be changed to the extent of not allowing A and B to meet or, at the very least, of preventing A from seeing B. Then, since nothing in a Reality made un-Real can be detected, A never has met B. Similarly, in every apparent paradox of Time-travel, Reality always changes to avoid the paradox and we come to the conclusion that there are no paradoxes in Time-travel and that there can be none."

Sennor looked well pleased with himself and his exposition, but Twis sell rose to his feet.

Twis sell said, "I believe, gentlemen, that time presses."

Far more suddenly than Harlan would have thought the lunch was over. Five of the subcommittee members filed out, nodding at him, with the air of those whose curiosity, mild at best, had been assuaged. Only Sennor held out a hand and added a gruff "Good day, young man" to the nod.

With mixed feelings Harlan watched them go. What had been the purpose of the luncheon? Most of all, why the reference to men meeting themselves? They had made no mention of Noys. Were they there, then, only to study him? Survey him from top to bottom and leave him to Twissell's judging?

Twissell returned to the table, empty now of food and cutlery. He was alone with Harlan now, and almost as though to symbolize that he wielded a new cigarette between his fingers.

He said, "And now to work, Harlan. We have a great deal to do."

But Harlan would not, could not, wait longer. He said flatly, "Before we do anything, I have something to say."

Twissell looked surprised. The skin of his face puckered up about his faded eyes, and he tamped at the ash end of his cigarette thoughtfully.

He said, "By all means, speak if you wish, but first, sit down, sit down, boy."

Technician Andrew Harlan did not sit down. He strode up and back the length of the table, biting off his sentences hard to keep them from boiling and bubbling into incoherence. Senior Computer Laban Twissell's age-yellowed pippin of a head turned back and forth as he followed the other's nervous stride.

Harlan said, "For weeks now I've been going through films on the history of mathematics. Books from several Realities of the 575th. The Realities don't matter much. Mathematics doesn't change. The order of its development doesn't change either. No matter how else the Realities shifted, mathematical history stayed about the same. The mathematicians changed; different ones switched discoveries, but the end results-- Anyway, I pounded a lot of it into my head. How does that strike you?"

Twissell frowned and said, "A queer occupation for a Technician?"

"But I'm not just a Technician," said Harlan. "You know that."

"Go on," said Twissell and he looked at the timepiece he wore. The fingers that held his cigarette played with it with unwonted nervousness.

Harlan said, "There was a man named Vikkor Mallansohn who lived in the 24th Century. That was part of the Primitive era, you know. The thing he is known best for is the fact that he first successfully built a Temporal Field. That means, of course, that he invented Eternity, since Eternity is only one tremendous Temporal Field shortcircuiting ordinary Time and free of the limitations of ordinary Time."

"You were taught this as a Cub, boy."

"But I was not taught that Vikkor Mallansohn could not possibly have invented the Temporal Field in the 24th Century. Nor could anyone have. The mathematical basis for it didn't exist. The fundamental Lefebvre equations did not exist; nor could they exist until the researches of Jan Verdeer in the 27th Century."

If there was one sign by which Senior Computer Twissell could indicate complete astonishment, it was that of dropping his cigarette. He dropped it now. Even his smile was gone.

He said, "Were you taught the Lefebvre equations, boy?"

"No. And I don't say I understand them. But they're necessary for the Temporal Field. I've learned that. And they weren't discovered till the 27th. I know that, too."

Twissell bent to pick up his cigarette and regarded it dubiously. "What if Mallansohn had stumbled on the Temporal Field without being aware of the mathematical justification? What if it were simply an empirical discovery? There have been many such."

"I've thought of that. But after the Field was invented, it took three centuries to work out its implications and at the end of that time there was no one way in which Mallansohn's Field could be improved on. That could not be coincidence. In a hundred ways, Mallansohn's design showed that he must have used the Lefebvre equations. If he knew them or bad developed them without Verdeer's work, which is impossible, why didn't he say so?"

Twissell said, "You insist on talking like a mathematician. Who told you all this?"

"I've been viewing films."

"No more?"

"And thinking."

"Without advanced mathematical training? I've watched you closely for years, boy, and would not have guessed that particular talent of yours. Go on."

"Eternity could never have been established without Mallansohn's discovery of the Temporal Field. Mallansohn could never have accomplished this without a knowledge of mathematics that existed only in his future. That's number one. Meanwhile, here in Eternity at this moment, there is a Cub who was selected as an Eternal against all the rules, since he was overage and married, to boot. You are educating him in mathematics and in Primitive sociology. That's number two."

"Well?"

"I say that it is your intention to send him back into Time somehow, back past the downwhen terminus of Eternity, back to the 24th. It is your intention to have the Cub, Cooper, teach the Lefebvre equations to Mallansohn. You see, then," Harlan added with tense passion, "that my own position as expert in the Primitive and my knowledge of that position entitles me to special treatment. Very special treatment."

"Father Time!" muttered Twissell.

"It's true, isn't it? We come full circle, _with my help_. Without it..." He let the sentence hang.

"You come so close to the truth," said Twissell. "Yet I could swear there was nothing to indicate--" He fell into a study in which neither Harlan nor the outside world seemed to play a part.

Harlan said quickly, "Only close to the truth? It is the truth." He could not tell why he was so certain of the essentials of what he said, even quite apart from the fact that he so desperately wanted it to be so.

Twissell said, "No, no, not the exact truth. The Cub, Cooper, is not going back to the 24th to teach Mallansohn anything."

"I don't believe you."

"But you must. You must see the importance of this. I want your co-operation through what is left of the project. You see, Harlan, the situation is more full circle than you imagine. Much more so, boy. Cub Brinsley Sheridan Cooper is Vikkor Mallansohn!"