“Well, Professor Lang?” Merada was addressing her. “What do you think?”

I think I’m an idiot. But Darya did not say it. She, who had mixed with Zardalu and a dozen other alien forms, had been so put off by minor human variations that she had not even been listening! For all she knew, everyone on Jerome’s World looked like Quintus Bloom.

“I’m sorry. What was that again?”

Professor Merada, heavy and humorless, nodded as though confirming some private suspicion. “Our guest was suggesting that perhaps it is a mistake to issue the fifth edition of the Artifact Catalog. It might be out of date, even before it appears.”

That was enough to grab Darya’s attention — all her attention. The Lang Catalog — her catalog! — was the Institute’s most respected publication. If Merada was considering withdrawing it, the influence of Quintus Bloom went far deeper than Darya had realized.

“It’s certainly not out of date! The new theory is wrong.” Darya noticed the change in the room as she spoke. Others had arrived while she was preoccupied with Quintus Bloom. She glanced along the table. Every face was familiar to her; even E. Crimson Tally’s, although it was anyone’s guess as to how the embodied robot had found his way in to what was supposed to be an invited dinner. And all those faces were turned in her direction, with every other conversation at the table abandoned.

Darya had had four hours between the end of the seminar and the start of the dinner. Not long, but enough to go back to her notes and review her own analyses.

“I say that the Builders are from the past, and existed millions of years ago. Whether they ceased to exist, or whether they now exist on some other plane that is beyond our senses, is not important. They were here, in the spiral arm. They made the artifacts. The Builders were certainly far different from us, in ways that we may never understand. They were masters of both space and time, and perhaps they could predict future events as we cannot. Furthermore, their artifacts call for a technology beyond our own, and possible changes to our understanding of the laws of physics. But that is all.”

Darya glanced again along the table. She had everyone’s attention. Quintus Bloom was smiling slightly, and Carmina Gold was nodding. E. Crimson Tally seemed slightly puzzled, as though what Darya had said was self-evident.

“Now compare that with what you are suggesting.” Darya glared at Bloom. “The Builders, you say, are from the future. But that is not an explanation of the Builders, it is merely a source of paradox. Let me make my point simply, by asking: Which future? If you say that they are from, say, Future A, then by coming back and planting the artifacts they will have created a different future for the spiral arm, say, Future B. If you reply that they did not create a different future, then Future A must be unaffected by the appearance of the artifacts; if it is unaffected, then there was no point to introducing the artifacts. Time travel as an explanation always has this fatal flaw: it contains the seeds of its own logical destruction. My ideas may require changes to the laws of physics. Yours are inconsistent with the laws of logic, and that is a far more serious problem.”

It was not coming out quite right. Somehow her clear thoughts were being twisted on the way from brain to lips.

Quintus Bloom was still smiling, and now he was shaking his head.

“But my dear Professor Lang, why are you so convinced that our present understanding of logic is any better than our understanding of physics? You asked us all a question. Let me now ask you a couple. First, does anything in your ideas explain the appearance of the new artifact, Labyrinth?”

“I don’t know that it’s new. I have had no chance to inspect it.” That was a weak answer, and Darya knew it.

“But I have done so, in detail. However, since you have not seen Labyrinth, let us omit it from consideration. Will you admit that there are changes in other artifacts, profound changes, more than there have ever been before?”

“I agree that there have been some changes. I’m not sure how great they are.”

“And do your theories explain why there have been changes?”

“Not yet. I came back to the institute to start a new investigation, precisely to explore those anomalies.”

“Ah. A worthy objective. But I can explain them now, without that research program. You say there have been ‘some’ changes. Professor Lang, when did you last visit an artifact?”

“I came here directly from the Torvil Anfract. It is an artifact.”

“Indeed?” Bloom’s eyebrows raised, and he glanced along the table. “But it is not listed in the famous Lang Catalog, the volume which we all take as our final authority.” He turned to Merada. “Unless someone with greater knowledge can correct my memory…”

“It’s not in the Catalog,” snapped Darya.

“Not even in the upcoming fifth edition? The new edition?”

“It is not in the Catalog,” Merada said. “Distinguished guest—”

“Please. Call me Quintus.”

“If you prefer it. Quintus, the Torvil Anfract had never been proposed as an artifact, until Professor Lang did so a moment ago. And it will never be listed as an artifact, without my personal review of the evidence.” Merada glanced reproachfully at Darya.

Bloom was still smiling benignly. “Very well, let us leave the Anfract for the moment. I want to ask Professor Lang: When did you last visit any Builder artifact other than the Torvil Anfract? One that is in the famous Lang Catalog.”

Darya thought back. Genizee, not in the Catalog. Serenity, not in the Catalog. The Eye of Gargantua, not in the Catalog. Glister, not in the Catalog.

“About half a year ago. The Umbilical, between Quake and Opal.”

“But the greatest changes to the artifacts have taken place within that time! Half a year, in which you have not seen a single artifact. Half a year, in which—”

Bloom paused. He lost his smile, turned, and stared to his right along the table. The voice of a puzzled embodied computer was steadily becoming louder.

“If the Builders are not in the future, then they can’t come back and change the present so that the Builders are in the future, because they are not there to do it.” E. Crimson Tally was staring down at the table top. “But if they are in the future, then the present didn’t need the artifacts to become that future, so then the future they make if they send the artifacts back is a different future—”

He paused and froze, his eyes blank and his mouth hanging open far enough to reveal his bottom teeth.

“There!” Darya pointed accusingly at Quintus Bloom. “Now you’ve done it. You’ve put E.C. into a loop. That’ll be hell to fix. I told you it was a logical contradiction, the idea that the Builders might have come from the future.”

She seemed to be the only one who cared. Half-a-dozen conversations were starting up along the table.

Professor Merada leaned over and patted her hand. “We are all good scientists here, Professor Lang, and it is as good scientists that we must behave. We all have our cherished theories, on which we have worked for many days and months and years. Although it is hard to abandon beloved ideas, if a new and better theory comes along it is our duty as good scientists to accept it. Even to embrace it.”

Darya bristled. The man was trying to soothe her. And Carmina Gold was nodding agreement. So were half a dozen others at the table. Darya couldn’t believe it. They had been here for less than a quarter of an hour. The first course of the meal was still to arrive, and she had said only a tenth of what she had to say — and badly, at that. But minds along the table were already closing. Darya had lost the argument. Quintus Bloom had won it.