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.”