"The details do not matter. He succeeded after mountains of drudgery and improvisation and took the generator to the California Institute of Technology, just as years before he had expected the real Mallansohn to do.

"You know the story from your own studies. You know of the disbelief and rebuffs he first met, his period under observation, his escape and the near-loss of his generator, the help he received from the man at the lunch counter whose name he never learned, but who is now one of Eternity's heroes, and of the final demonstration for Professor Zimbalist, in which a white mouse moved backward and forward in time. I won't bore you with any of that.

"Cooper used the name of Vikkor Mallansohn in all this because it gave him a background and made him an authentic product of the 24th. The body of the real Mallansohn was never recovered.

"In the remainder of his life, he cherished his generator and cooperated with the Institute scientists in duplicating it. He dared do no more than that. He could not teach them the Lefebvre equations without outlining three Centuries of mathematical development that was to come. He could not, dared not hint at his true origin. He dared not do more than the real Vikkor Mallansohn had, to his knowledge, done.

"The men who worked with him were frustrated to find a man who could perform so brilliantly and yet was unable to explain the whys of his performance. And he himself was frustrated too, because he foresaw, without in any way being able to quicken, the work that would lead, step by step, to the classic experiments of Jan Verdeer, and how from that the great Antoine Lefebvre would construct the basic equations of Reality. And how, after that, Eternity would be constructed.

"It was only toward the end of his long life that Cooper, staring into a Pacific sunset (he describes the scene in some detail in his memoir) came to the great realization that he was Vikkor Mallansohn; he was not a substitute but the man himself. The name might not be his, but the man history called Mallansohn was really Brinsley Sheridan Cooper.

"Fired with that thought, and with all that implied, anxious that the process of establishing Eternity be somehow quickened, improved, and made more secure, he wrote his memoir and placed it in a cube of Time-stasis in the living room of his house.

"And so the circle was closed. Cooper-Mallansohn's intentions in writing the memoir were, of course, disregarded. Cooper must go through his life exactly as he had gone through it. Primitive Reality allows of no changes. At this moment in physiotime, the Cooper you know is unaware of what lies ahead of him. He believes he is only to instruct Mallansohn and to return. He will continue to believe so until the years teach him differently and he sits down to write his memoir.

"The intention of the circle in Time is to establish the knowledge of Time-travel and of the nature of Reality, to build Eternity, ahead of its natural Time. Left to itself, mankind would not have learned the truth about Time before their technological advances in other directions had made racial suicide inevitable."

Harlan listened intently, caught up in the vision of a mighty circle in Time, closed upon itself, and traversing Eternity in part of its course. He came as close to forgetting Noys, for the moment, as he ever could.

He asked, "Then you knew all along everything you were to do, everything I was to do, everything I have done."

Twissell, who seemed lost in his own telling of the tale, his eyes peering through a haze of bluish tobacco smoke, came slowly to life. His old, wise eyes fixed themselves on Harlan and he said reproachfully, "No, of course not. There was a lapse of decades of physiotime between Cooper's stay in Eternity and the moment when he wrote his memoir. He could remember only so much, and only what he himself had witnessed. You should realize that."

Twissell sighed and he drew a gnarled finger through a line of updrafting smoke, breaking it into little turbulent swirls. "It worked itself out. First, I was found and brought to Eternity. When, in the fullness of physiotime, I became a Senior Computer, I was given the memoir and placed in charge. I had been described as in charge, so I was placed in charge. Again in the fullness of physiotime, you appeared in the changing of a Reality (we had watched your earlier analogues carefully), and then Cooper.

"I filled in the details by using my common sense and the services of the Computaplex. How carefully, for instance, we instructed Educator Yarrow in his part while betraying none of the significant truth. How carefully, in his turn, he stimulated your interest in the Primitive.

"How carefully we had had to keep Cooper from learning anything he did not prove he had learned by reference in the memoir." Twissell smiled sadly. "Sennor amuses himself with matters such as this. He calls it the reversal of cause and effect. Knowing the effect, one adjusts the cause. Fortunately, I am not the cobweb spinner Sennor is.

"I was pleased, boy, to find you so excellent an Observer and Technician. The memoir had not mentioned that since Cooper had no opportunity to observe your work or evaluate it. This suited me. I could use you in a more ordinary task that would make your essential one less noticeable. Even your recent stay with Computer Finge fitted in. Cooper mentioned a period of your absence during which his mathematical studies were so sharpened that he longed for your return. Once, though, you frightened me."

Harlan said, at once, "You mean the time I took Cooper along the kettle ways."

"How do you come to guess that?" demanded Twissell.

"It was the one time you were really angry with me. I suppose now it went against something in the Mallansohn memoir."

"Not quite. It was just that the memoir did not speak of the kettles. It seemed to me that to avoid mention of such an outstanding aspect of Eternity meant he had little experience with it. It was my intention therefore to keep him away from the kettles as much as possible. The fact that you had taken him upwhen in one disturbed me greatly, but nothing happened afterward. Things continued as they should, so all is well."

The old Computer rubbed one hand slowly over the other, staring at the young Technician with a look compounded of surprise and curiosity. "And all along you've been guessing this. It simply astonishes me. I would have sworn that even a fully trained Computer could not have made the proper deductions, given only the information you had. For a Technician to do it is uncanny." He leaned forward, tapped Harlan's knee lightly. "The Mallansohn memoir says nothing about your life after Cooper's leaving, of course."

"I understand, sir," said Harlan.

"We will be free then, in a manner of speaking, to do as we please with it. You show a surprising talent that must not be wasted. I think you are meant for something more than a Technician. I promise nothing now, but I presume that you realize that Computership is a clistinct possibility."

It was easy for Harlan to keep his dark face expressionless. He had had years of practice for that.

He thought: An additional bribe.

But nothing must be left to conjecture. His guesses, wild and unsupported at the start, arrived at by a freak of insight in the course of a very unusual and stimulating night, had become reasonable as the result of directed library research. They had become certainties now that Twissell had told him the story. Yet in one way at least there had been a deviation. Cooper was Mallansohn.

That had simply improved his position, but, wrong in one respect, he might be wrong in another. He must leave nothing to chance, then. Have it out! Make certain!

He said levelly, almost casually, "The responsibility is great for me, also, now that I know the truth."