Killing everybody aboard would obviously include the mice, unless Noxon took them with him into the future. Which he clearly had no intention of doing, since they could not be trusted.
The mice started a few feeble protests. But Noxon could hear them convincing each other that the plan made sense.
“There isn’t a hundred thousand years of life support for us, even though our needs are few,” said a spokesman for the mice. “Covered with ice, it would be very difficult to do the necessary air exchange. But instead of killing us, you should bring us with you.”
“Nice try,” said Noxon. “Even if you don’t take over the ship, all you have to do is start having babies while humans are still evolving, and if you permit us to survive at all, I have a feeling it will still be a world run by mice.”
“We promise we won’t!” cried the mouse in despair.
“I think they have to get back in the box,” said Noxon. “Then we give them a week, to give us time to get back from the future, send for the flyer, and return to take off again. So, my dear expendable,” he said, “will you take care of shutting down all life support on the ship a week after we leave?”
“Will I really have to do it?” said the expendable. “Won’t you be back before the week is up?”
Noxon shook his head. “You have to live through the version of events in which we don’t come back. But when we do come back, the version of you that we meet will never experience the complete shutdown, so that version will be sure that you never had to kill the mice and the colonists.”
“That doesn’t make sense,” said Ram Odin. “I take your word for it, but…”
“I exist at all,” said Noxon, “because there was a version of me, Rigg Sessamekesh, that killed a version of you, Ram Odin—a much older version—in order to keep him from killing me first. That actually happened, and the version of me that is still called Rigg actually did the killing. Just as a version of the expendable will shut down the life support and observe as the mice and all the colonists die.”
“So does that mean there’ll be two of me?” asked the expendable.
“No,” said Noxon. “Because once this ship goes cold, it’s completely out of the causal chain. When we return, nothing that happened after we left will have affected Ram and me in any way. So the dead version of the ship won’t exist once we make the change.”
“You say that as if you knew what you were talking about,” said Ram Odin.
“Because I do know,” said Noxon. “The only person who gets copied is the one who is part of the causal chain. So when Rigg prevented himself from killing that older version of you, Ram, it created a second Rigg—me, the one that didn’t kill you—but not a second Ram Odin.”
“Except here I am,” said Ram Odin.
“You’re the twentieth Ram Odin left over from an earlier division, and you know it,” said Noxon. “You’re just being frivolous.”
“I am,” said Ram Odin. “I think the plan will work.”
“You talk about trusting us!” cried the mice. “But how can we trust you!”
“The mice are having trust issues,” said Noxon.
“The first time they tried to take over the ship, they signed their death warrants,” said Ram Odin. “Even if we never come back, they’ve had a day of life that they didn’t deserve.”
“Here’s why you can trust us,” said Noxon to the mice. “First, unlike you, we haven’t broken our word over and over again. Second, I could have you killed at any time and I haven’t, so why would I need to go to all this elaborate preparation to kill you now? If I don’t want you alive, you’re dead whenever I want. You can’t hide on my body if I take off my clothes, and you can’t hide anywhere else because the expendable can turn off the life support.”
“So I’m giving you continuous evidence that I am committed to your survival—provided you don’t endanger the survival of the human race, which means you stay in this ship and die with it.”
“I don’t know why you brought the mice along in the first place,” said Ram Odin.
“Because two of the wallfolds on Garden are shared with billions of sentient mice. I may need these as witnesses of what we do here. Or if I conclude that we do have to destroy the human race on Earth, then the mice can do it more easily and thoroughly than I can.”
“You’re the version of Rigg that isn’t murderous?” said Ram Odin.
“I’m here to save Garden,” said Noxon. “And it’s humans from Earth who destroy it. You do the math.”
“It’s ironic, that’s all,” said Ram Odin. “We created colony ships because that comet came so close to the kind of impact that would destroy all life on Earth. We had to create a colony so humans would exist on more than one world. And now you come back and destroy the human race on Earth.”
“I’ve come back to find out why Earth decided to destroy Garden,” said Noxon, “and talk them out of it, if I can. But I’m going to save the nineteen wallfolds of Garden, one way or another. Humanity may have arisen here, but that doesn’t mean they have a right to destroy Garden after 11,191 years of history there.”
“I agree,” said Ram Odin. “I’m just noting the irony.”
“Noted,” said Noxon.
“I’m afraid to die,” said one of the mice.
“You would hardly be sentient if you weren’t,” said Noxon. “But you are sentient, and that’s why I’m not going to leave you here, dead. I’m going to change the future if I can. Either way, I’ll come back and get you. Just remember that you will die, the first time through. But when I retrieve you, you’ll have no memory of that death. And you’ll know, once again, that I keep my word—even though you don’t.”
“So it’s settled,” said Ram Odin. “We park the ship where ice will cover it. Then you and I leave the ship and use the flyer to get us to a place that will someday be reasonably well-inhabited. From there we travel into the future, while the flyer—and our expendable friend—go back to the starship, kill everybody, and shut down all the systems. But we return in time to stop any of that from happening.”
“That’s the plan,” said Noxon.
“Only one problem,” said Ram Odin. “Fuel.”
“Oh?” asked Noxon.
“This ship can set down on a planetary surface,” said Ram Odin. “But on Garden, it was a bit of a sharp collision, right?”
“An extinction-level event,” said the expendable. “By design.”
“If we land more gently and nondestructively, can we get back up into space?” asked Ram Odin.
“We have been performing those calculations during your discussion of the ethics of temporary musicide,” said the expendable. “Since we made the return voyage to Earth without expending any fuel at all, and we began that voyage halfway through the huge energy expenditure of creating the fold and leaping into it, we definitely have enough fuel for a trivial task like rising from the surface of a small rocky planet and getting back to scoop velocity.”
Noxon had learned enough to know this meant the speed at which the powerful collection field could be extended to gather interstellar hydrogen and other dust to turn it into the plasma that fueled the ship.
“Then I think we’re all set,” said Noxon. “All that remains is to choose the right time. For that, Ram and I need to leave the ship for a while. And that means that the mice go back into the box.”