“So you’re arguing in favor of xenocide?” asked Ram.

“Not at all,” said Wheaton, looking horrified. “Nothing of the kind! Garden has endured for eleven millennia with tight restrictions on their ability to develop high technology, right?”

“Yes,” said Noxon.

“And that was a lid placed on the planet by other humans, right?”

“By computers,” said the expendable, “but obeying human orders.”

“So if we go into the past and put such a lid on both these species,” said Wheaton, “we’re doing to them nothing that we haven’t already done to ourselves.”

“To one portion of our species,” said Noxon. “Earth didn’t put any such lid on themselves.”

“We don’t have to destroy their whole biota in order to set up colonies here, do we?” asked Wheaton.

“It depends on what proteins they produce, and whether we can digest enough of them,” said Ram.

“I don’t suppose now would be a good era in which to make our investigations,” said Wheaton.

“You want to go into the past and see them early in their evolution,” said Noxon.

“I am what I am,” said Wheaton. “But I’m also right.”

“Put us back a few hundred thousand years ago,” said the alpha mouse, “and we’ll be their lid.”

“The mice have already suggested,” said Noxon, “that ten of our ships go to the other world, and ten stay here.”

“I wonder if versions of you are saying exactly the same thing on all nineteen of the other ships,” said Ram.

The expendable answered. “The exact wording is quite different, but yes, on every ship you have reached approximately the same point in your discussion.”

“What have the others decided?” asked Ram.

“They’re all asking their expendables what the others decided.”

“We haven’t decided anything,” said Wheaton. “But the only sensible thing is to go back in time, split the fleet in half, and explore both worlds to see what damage we might have to do in order to use them.”

“But we don’t even know what the sentient species look like on either world,” said Noxon. “How will we know which life forms in the past are going to evolve into them?”

“We have images of both species,” said the expendable. “Both worlds are regularly broadcasting visuals using primitive raster scans.” Holograms appeared in the middle of the cockpit. One species was low to the ground, with many limbs, all of them ­capable of grasping, and many of them with sharp claws or blades at their fingertips. The other species was tripedal, tall, and gracile, with a head crowned with vicious-looking horns. All three feet were prehensile, and one of them had two thumblike projections.

“Let me guess,” said Ram. “The low, scuttling one is the aggressive species that’s trying to take over the other side’s computers.”

“Wrong,” said the expendable.

“You wanted the roachlike one to be evil,” said Wheaton, delighted. “Easier to hate them!”

“Oh, I could easily hate them both,” said Ram. “For all we know, they teamed up to attack us. We never saw who was piloting those aircraft.”

“It’s too dangerous to go into the future to see what happens,” said the alpha mouse. “Our counterparts on the twentieth ship are still searching to make sure they’ve cleaned out all the intrusions.”

“The mice don’t want to go into the future to learn any more,” said Noxon. “If they’re scared of the aliens’ capabilities, we’d be crazy to make the attempt.”

“So we just go blindly backward,” said Ram.

“To find out if we can leave the flora and fauna on either world intact,” said Wheaton.

“We can,” said Noxon. “We can always decide not to establish colonies on either world.”

“That’s not an option,” said Ram. “We’re here to neutralize the threat. We have no way of monitoring whether we’ve succeeded without establishing a permanent, technologically powerful presence.”

“That’s not really true,” said Noxon. “For instance, we could drop off the mice a million years ago and then pop back to this time to see where we stand.”

Ram laughed. “We’d find that the mice were completely prepared to destroy us, take over our ship, fly back to Earth, and take over everything.”

“We would never,” said the alpha mouse.

“I was just pointing out that if we establish human colonies, it’s because we want to, not because there’s no other way,” said Noxon.

“Well,” said Ram, “whatever we do, I don’t propose to leave it all up to the mice.”

“The other ships have all decided to go back and test the proteins on both worlds,” said the expendable.

“How do we divide the fleet?” asked Ram.

“The computers have already divided the ships randomly into two groups of ten. We’re in the group that stays at this near world, while the others jump the fold to the far one.”

“The one with the tripods,” said Wheaton. “That’s a shame—I was most interested in studying them.”

“That’s how all the Wheatons felt,” said the expendable. “But then they all decided that both species need to be studied, so half the Wheatons have to take the second choice.”

Wheaton sighed. “I suppose for every Professor Wheaton who lost, there’s a Professor Wheaton that won.”

“Depending on how you define ‘won’ and ‘lost,’” said the expendable. “You could say that they all win, with an entirely new sentient species to study.”

“I feel much happier already,” said Wheaton.

“Ironic or sincere?” asked the expendable.

“Pissed off but compliant,” answered Wheaton.

Noxon sliced them through the time it took for the ship to fly into stationary orbit around the near planet. At Noxon’s insistence, the mice stayed on the ship with him and Ram, as Wheaton and the expendable flew down to the surface. “The scientist and the robot can do the job perfectly,” said Noxon. “The time traveler and the pilot have to stay here, in case we have to undo something horrible the mice have done.”

“So untrusting,” said the alpha mouse.

Noxon regarded this comment as not worth answering.

Wheaton and the expendable made frequent reports during their days of data collection. Ancestors of the scuttling aliens were easy enough to spot—they were already as close to sentience as, say, Homo habilis. Using tools, but not yet making fire. “It is difficult for Professor Wheaton to stay focused on the project at hand,” said the voice of the ship. “He keeps wanting to go backward and forward and the expendable has to keep reminding him that only Noxon can do that.”

During one of the lulls between reports, while Ram was exercising, Noxon said, more to himself than to Ram, “I miss Deborah.”

Ram didn’t answer, but the alpha mouse did. “Why didn’t you simply copy her and bring her along? There’d be twenty of her now. Plenty to go around.”

“She wanted eyes,” said Noxon. “The twenty who came with us would be disappointed for the rest of their lives.”

“What?” asked Ram. Now he heard.

“Just talking with the mice,” said Noxon.

“Whatever you say to them, they’re going to use against you later,” said Ram.

“Unless we use it for you,” said the alpha mouse.

“He can’t hear you,” murmured Noxon.

“I wasn’t talking to him,” said the alpha.

“I’ll eventually find someone among the colonists,” said Noxon. “I’m not worried.”

“You’re really strange-looking,” said the alpha. “Most of the colonists will be completely repulsed by you.”

“Is that why all the females were pregnant five times over before they came on this voyage?” asked Noxon. “So they wouldn’t have to do something as repulsive as mate with a small-testicled male like you? Or was I right that you were castrated?”

“I don’t have body-image issues the way humans do,” said the alpha.

“No, you don’t have any kind of shame at all,” said Noxon.

“Someday you’ll understand us,” said the alpha.