“What is unique about our own time, sufficient to cause a basic change in Builder artifacts — in all Builder artifacts? Why did the new artifact, which I described yesterday and called Labyrinth, come into existence?”

A new artifact? But every one was at least three million years old! Bloom must mean there was a newly-discovered artifact. Even that was hard to believe. Darya had scoured every record in the spiral arm. She wanted to interrupt, to make Bloom stop and repeat whatever it was he had said the previous day. But she could not do it, and he was sweeping on:

“I want to suggest an answer, and also to make a prediction. The changes are occurring because the artifacts have at last achieved their intended purpose.

“And what is that intended purpose? It is to shape the development of the spiral arm, so that it follows a certain path into the future. Now we can ask, how is it possible that the Builders knew what shape the future might take?

“To answer that question, I return to my earlier point. The Builders, we know, had a mastery over space and time that is far beyond us. It is far beyond us, literally, because the Builders are not from the distant past, an ancient race who built their artifacts and then somehow vanished. They are from the future, the far future, where they built the artifacts and returned them to the past. The Builders are beings from the future, who have mastered time travel. Let me say that again, in other words, because it is so important. The Builders did not vanish from the spiral arm at some time in the past. They were never in the arm in the past — that is why we find no trace of them there. They are in the future.

“And which beings are they? Given their interest in human affairs, and the way that they have shaped human affairs, there is only one plausible answer: the Builders are us — our own distant descendants. We are, or will be, the Builders.

“And so, my overall prediction: the Builder artifacts have achieved their main purpose, steering us along the desired path of spiral arm development. Since that primary purpose is fulfilled, the Builder artifacts will continue to change, and even to disappear from existence. They will return whence they came — to the future.”

The lecture hall was in an uproar. Only Merada, who had known what was coming, remained calm. Quintus Bloom was standing at the front of the stage, gesturing at Darya.

“I wonder, Professor Lang.” His voice carried over the hubbub. “I wonder if you have any comments. I would appreciate your opinion.”

But Darya’s mind was spinning. She could not give her opinion. Not because Bloom’s suggestion that the Builders were time travelers from humanity’s own future was unthinkable.

No. Because Darya had considered that possibility herself, long ago — and rejected it, for reasons too subtle to present off the cuff, and in public. She shook her head at Quintus Bloom, turned and began to push her way back toward the entrance. She had to think. If there really was a new artifact, as he had suggested, she had to find out all there was to know about it; then she had to re-evaluate everything she had ever thought and done in her whole blessed career.

“So that was it. The talk by Quintus Bloom left Darya fit to burst. Anyone could tell that by looking at her. After she’d had a session or two with Bloom she took off. Left Sentinel Gate.”

Hans Rebka stopped speaking. He showed no signs of starting again.

Louis Nenda, who had been offering pheromonal simultaneous translation for the benefit of Atvar H’sial, glared at him. The transition had been abrupt, from detailed description to a sudden two sentence cut-off. It was certainly not a logical end point.

“Are you saying that’s it? That’s all you’re going to say about what happened, and where and why she went?”

Rebka shrugged. “I’ve told you all I know.”

“And you let her go, just like that. Didn’t try to talk her out of it, or stop her, or go with her?”

“I didn’t.”

“He is lying, Louis.” The pheromonal message from Atvar H’sial came quickly. It was not necessary.

“Damn right he’s lying. But why?” Out loud he said, “Were you in on the sessions she had with Quintus Bloom?”

Rebka shrugged. “I sat in on the seminar, until it was clear to me that I wasn’t going to understand more than three words.” He looked Nenda straight in the eye. “I don’t know what they said to each other.”

Nenda stared right back. “I believe you.” He added to Atvar H’sial, “In a pig’s eye. I can lie with a straight face as well as anybody. What now, At?”

“We have something of a problem, Louis. I do not wish to reveal to him that Bloom’s prediction, of changing and vanishing artifacts, appears to be coming true.”

Hans Rebka snapped his fingers. “Oh, there was one other thing that will interest you, Nenda. Soon after we arrived at Sentinel Gate, J’merlia and Kallik rolled up at the institute.”

As a distraction, it was first-rate. Nenda went pop-eyed. “Kallik is here now? And J’merlia? Why didn’t you tell us that before?”

“Because they aren’t here now. Darya took them with her.”

“She can’t do that! They don’t belong to her. They belong to me and Atvar H’sial.”

“Not any more. They have the rights of free beings.”

“Nuts. I have their slave cubes, right here.” Nenda began to fumble at his tight head-to-toe clothing, which proved almost as hard to get into as it was uncomfortable.

“Louis, what is going on?” The exchange between Nenda and Rebka had been too fast for Atvar H’sial to receive a pheromonal translation.

“J’merlia and Kallik. Been here — and gone. With Darya Lang.”

“My J’merlia!”

“And my Kallik. I know what I said, At, but we better be ready for more than a day’s stay. You and me got lots of work to do before we can leave Sentinel Gate.”

Hans Rebka had told the truth about Darya’s first encounter with Quintus Bloom, and what happened afterwards (even if it was not, for reasons that Hans preferred to keep to himself, the whole truth).

She had run from the lecture hall, so swamped with emotions that her mind refused to function. But ten minutes later she was pushing her way back in, barging past the same angry people as on her first entrance. Wrong or right, Quintus Bloom had not finished, and she had to hear the rest of it.

She knew there had to be more, if Quintus Bloom was to retain his plausibility with Professor Merada and the institute. Merada, whatever his faults, was scrupulously honest and painstakingly thorough.

Darya herself had long ago noted — and remarked on — the mastery of time and space exhibited in the Builder artifacts. It was easy to form a theory around the idea that the Builders had time travel. But theories were a dime a dozen. The partition that separated science and wishful thinking was evidence: observations and firm facts.

The odd thing was that Quintus Bloom had facts, more than Darya would have believed. As he spoke she became convinced. The artifact near Jerome’s World, whether it was new or not, certainly existed. Bloom had visited Labyrinth, and found a way to penetrate its coiled and re-entrant geometry. He had taken recording equipment with him. At the key moment of his presentation, the darkened stage of the research institute filled with scenes of Labyrinth: the scan from all angles, and the bizarre interior where nothing remained still and nothing followed straight lines.

Quintus Bloom kept his comments to a minimum. He allowed the images to speak for themselves, until at last he said, “This is the innermost chamber of Labyrinth. The scenes that follow are taken directly from polyglyphs contained within that chamber. I have performed no editing, no adding to or subtracting from. I merely display what I found revealed on the chamber walls.”