“You don’t have a place on Earth anymore,” said Noxon. “There’s a girl with eyes using your name and fingerprints, Deborah, and a charming philologist who has done rather a good job of keeping a dying discipline alive who needs no competing Dr. Wheaton.”

“Especially since there’s no record of my degrees or my publications,” said Wheaton. “It rather blocks my ability to influence what passes for thinking among this sorry crop of anthropologists.”

“I can offer you each your choice of improbable futures. You can voyage to the alien world and take part in the discussions, though not the decisions, about what we will do to prevent the destruction of Earth. Or you can voyage to Garden, my home, where I can promise you will have access to the full range of studies of—”

Deborah interrupted him. “For me, there’s no choice but the world where I can get new eyes.”

“You do understand,” said Noxon, “that you might be unable to control the facemask. It’s not a matter of what humans call ‘strength of will.’ Some of the strongest people I know have been unable to tame the mask. If you get eyes, but cease to be yourself, it would be a poor bargain.”

“Then you’ll go back in time and prevent it,” said Deborah.

“But there you’ll be in a world without replacement batteries, without charging stations.”

“They’re solar. We’re not Neanderthals.” She gave Wheaton an exaggerated wink, to prevent his objection to her pejorative use of “Neanderthal.”

“They’re solar, but not unbreakable,” said Noxon. “Garden is not a very good place to be blind.”

“I will bring spares,” said Deborah.

“And the technology of our era is available,” said Wheaton. “Each starship should have the ability to replicate her glasses.”

“I didn’t think of that,” said Noxon.

Deborah raised a hand. “Something else must be said, however. Just because I will go to Garden or nowhere, that doesn’t mean you must go with me, Father. The chance to study the evolution of two alien species—I think that not only will you enjoy that voyage more, you might actually be able to offer crucial insights as Noxon makes his decisions.”

“What insights?” said Wheaton. “I know Erectids and other anthropes, and nothing more.”

“You know how to see evolutionary patterns,” said Deborah. “You know how natural selection works, how different societies promote the survival of some traits and not others. And there have been no human scientists on that road before you.”

“Do I detect a desire to be rid of this old man?” asked Wheaton with a laugh.

“Do I detect a barely-concealed plea for validation?” asked Deborah. “You know I love you, and I’d like to think your work would not be possible without me to clerk for you. But that isn’t true, and besides, you can have the ship pop out an extra expendable to take notes and look things up for you. Much more efficiently and accurately than I would.”

“Very well, I suppose I can work without you,” said Wheaton. But he looked grumpy, and that seemed to be a concealment of an underlying hurt.

“One world offers me eyes,” said Deborah, “and the other offers you a chance to do seminal work. If Noxon and Ram succeed in changing the future of that world, you will be the only scientist to observe the alien society as it existed before human interference.”

“We won’t be doing much observation,” said Noxon. “Particularly if we reach them at a time when they’re already technologically ahead of us. We’ll skedaddle instantly then.”

“I’ve found that brave dead scientists don’t contribute as much as prudent live ones,” said Wheaton. “I’ll study what there’s time to study.”

“It’s where you want to go,” said Deborah.

“All things being equal. But . . . nineteen wallfolds. A species of merpeople! Either world will do for me.”

Deborah made no answer, even though both Noxon and Wheaton looked at her, waiting.

“You know I have a choice myself,” said Noxon. “There are two of me now. One who went through the nuclear blast but managed to heal from it. One who didn’t.”

“Which are you?” asked Deborah.

“I’m the one who was warned and saved from the blast,” said Noxon. “But my twin and I have worked it out. It’s quite simple, really. There’s some risk that he suffered damage to some or all of his gametes. The facemask heals damage it can detect, but it’s possible for gametes to be motile and yet not viable, or viable but mutated.”

“Ouch,” said Deborah.

“Mine, however, were unharmed,” said Noxon. “Not that there’s no risk of mutation or deformation—any gamete can be damaged by the vicissitudes of chance. But . . .”

“So you, Mister Pristine Sperm, will go where you think your seed will be most needed,” said Deborah.

“Not quite,” said Noxon. “Chances are that both of us will be able to reproduce successfully. But we want to invest my superior odds in a particular way.”

“I’m not sure why this is a matter for discussion with us,” said Wheaton.

“Excuse me, sir, but I’m discussing the possibility of marriage to your daughter,” said Noxon. “And explaining to you both why my twin and I have decided that where she goes, there go I. Not because we expect anything, or require anything. We’re both quite smitten with your daughter. In fact, we’re both very much in love with her. So on the chance that she might at some future point reciprocate . . .”

“Passage through the Wall apparently makes you awkward and stuffy in any language,” said Wheaton.

“We want to offer her the best chance of creating a family with healthy, whole, unmutated children.”

“Apart from that little genetic twist about being able to fiddle with time,” said Wheaton.

“We’re not sure whether that’s a plus or not,” said Noxon. “We do know that while pathfinding emerged at an early age, time manipulation came along much later. I don’t think that she would find a nursing baby suddenly disappearing and then reappearing at another time.”

“So you look at my breasts and think of attaching a baby to them?” asked Deborah.

Noxon looked at her steadily, trying to conceal his consternation. “I assure you that I’m a normal human male in most respects. But I’m an uxorious male, I believe the professor would say, and so I don’t have the alpha male’s assumption that all women are faunching to mate with me.”

“Only to nurse your babies.”

“Only to wish the babies they nurse to be healthy and not particularly weird.”

“What if I like your twin better than you?” asked Deborah. “Pretty cheeky, to take the decision out of my hands.”

“We’re quite sure that you can’t tell the difference between us at this point,” said Noxon. “And also sure that our feelings toward you are identical, because we were in love with you long before we duplicated.”

“When, exactly, did this overpowering passion first . . . overpower you?” asked Deborah.

“I first noticed it when you inconveniently got yourself killed by an Erectid stone.”

“Clumsy of me,” said Deborah.

“You didn’t follow instructions,” said Noxon. “And I knew, rationally, that I should consider the option of leaving that unfortunate event alone. But I did not consider it. I didn’t actually give a rat’s ass what else happened. Even if it would make saving Garden more difficult, I was not going to leave you dead.”

“How gallant,” said Deborah.

“I thought of going on without you and I found that unbearable,” said Noxon.

“Yet because one of you is going to Garden and the other to the planet Hell, or whatever we’re calling it, one of you must go on without me.”

“Yes,” said Noxon. “And so we decided, rationally, that we would offer you ourself at our best. My best. And the other would go about his tragic, meaningless existence without you.”

“And now you’re being ironic.”

“I’m being quite sincere,” said Noxon. “My twin is quite ­broken up about it. But he was the one who insisted that we make the decision on this basis—this rational basis—rather than drawing straws. Or making you choose, which would have been arbitrary and cruel to you.”