And then he was gone.

Umbo’s first impulse was to shout after Rigg and Loaf to stop. But he couldn’t hear their footsteps now. He wasn’t sure where they were, or if they would hear him. His broken, bleeding future self had said to do nothing. The future self presumably cared as much about Loaf and Rigg as Umbo did right now, so if he said to do nothing it was presumably because there was nothing useful to be done. If Umbo couldn’t trust his own future judgment in such a matter, whom could he trust?

How much of nothing was he required to do? Could he go back to Olivenko and warn him? Warn them, if Param had come out of hiding and caught up?

Surely that didn’t count as “something”—he could surely go back.

Yet every instinct pushed him forward, to follow Rigg and Loaf and see what was about to happen to them.

But it might be that nothing would happen. It might be only Umbo himself who was in such danger. Stay here, do nothing. If a future self came back to warn him, Umbo had no choice but to obey.

He stayed in place. He did nothing.

A few minutes later, he heard footsteps. He saw Param coming through the factory, and then Olivenko following her.

“Where did they go?” demanded Param.

“I don’t know,” said Umbo.

“Why aren’t you with them?”

“Because I came back from the future to warn myself not to go on.”

Param paused a moment, blinking slowly while she processed the implications of his statement.

“Do you have any idea why?”

“I only know that I never come back and warn myself unless it’s really important that I do exactly what I tell myself to do,” said Umbo.

“What about me?” demanded Param.

“Whatever the danger is, it probably already passed,” said Umbo.

“Danger?” asked Param.

“Probably?” asked Olivenko, who had just caught up.

“My future self was a mess. Broken arm, ear half gone, bleeding from a lot of places.”

“So you let my brother go on without a warning?” demanded Param.

“I did what I told myself to do,” said Umbo. “My future self could have given warning while we were still together. He came to me the very first moment that I was alone.”

“So the warning was for you,” said Olivenko. “Not Rigg and Loaf.”

“What if your future self is a lying traitor?” asked Param.

“What if your present self is an accusing idiot?” asked Umbo. So much for making a good impression on Param.

“So you’re just going to do what you’re told,” she said. “Hang back, like a coward.”

Resentment got the better of him. “Better than hiding the way you did,” said Umbo. “Turning invisible when there were things to decide. That was so brave of you.”

“If my brother gets hurt because you—”

“If I didn’t warn my friend Rigg,” said Umbo, “it was because he didn’t need a warning.”

“Or because a warning would do no good,” said Olivenko.

“You think Rigg is dead?” demanded Param.

“I think Umbo told us to wait here,” said Olivenko.

“And he’s boss of the expedition now?”

“Not me,” said Umbo. “My future me.”

“He must be from a long time in the future, if he’s smart enough to know what’s best for us to do.”

Umbo stood aside and gestured for her to go on. “By all means, find Rigg and save him, or die trying. I saw the condition my future self was in. You didn’t. So go ahead.”

“Stop it,” said Olivenko. “Neither of you knows anything, but future Umbo knew something, and that’s more than we know, so we’re going to do what he says.”

“You can’t stop me,” said Param.

“Think, Param,” said Olivenko. “You move far slower when you disappear. Whatever danger there is will be over by the time you get there.”

“Get where?” asked Umbo. “I could hear their footsteps, and suddenly I couldn’t. Yet they didn’t turn back to look for me. I think they went into some kind of passage and closed the door behind them.”

“It can’t hurt to look for that passage,” said Olivenko.

“I can think of lots of ways it can hurt,” said Param, “but I’m doing it anyway.” She strode out into the room.

“They were walking that way,” said Umbo, pointing.

“When you last saw them,” said Param.

“They were furtive. Walking near the wall. It’s a door in the wall.”

It turned out to be a stairway leading down into the floor, hidden in the shadows behind a tall piece of machinery.

“They’re looking for a starship, and they go down into the ground?” said Olivenko.

“We should, too,” said Param.

“We should wait,” said Umbo.

“They’re in danger.”

“And we’re safe,” said Umbo.

“How do you know that?”

“Because if it wasn’t safe for us to stay here, my future self would have told me to run like a bunny.”

“So something dangerous is happening down those stairs somewhere, and you’re going to sit here and do nothing?”

“That’s what I told myself to do,” said Umbo, “and I’ve decided to trust myself. Do what you want.”

What she wanted, after fuming and complaining a little longer, was apparently to pace back and forth but never go down the stairs.

Rigg noticed when Umbo fell behind, but he assumed that he would catch up. Rigg felt the same sense of awe at the huge machines, but he knew that if both boys stopped to look at them, Vadesh would be alone with Loaf and that’s what Vadesh wanted. Which meant that was the thing Rigg couldn’t allow to happen.

As usual, thought Rigg. Umbo feels free to be a child, easily distracted from the task at hand, while I keep my mind on what has to be done. But later, Umbo will resent me for taking responsibility.

I don’t take responsibility, I’m just left with responsibility in my hands and no one to help me carry it.

Which wasn’t fair. Loaf was there, wasn’t he? But Loaf was playing the risky game of taking Vadesh at his word, testing him.

At the bottom of the stairs was a tunnel, and in the tunnel there was a kind of wagon, though it had nothing to pull it and no cargo. But there were benches at the front and back, so people were meant to ride. Vadesh stepped onto the wagon and Loaf followed him.

“Umbo’s not here,” said Rigg.

“You wait for him and take the next wagon,” said Vadesh.

Rigg understood immediately that what Vadesh was really saying was good-bye. So he bounded onto the wagon. It was already moving forward when his feet hit the floor, accelerating so quickly that Rigg fell over and slid to the back of the wagon. Vadesh had somehow given the wagon the command to go while Rigg was still standing on the platform. If he had hesitated, if he had tried to call out to Umbo, anything but board the wagon at the instant that he did, Vadesh would have left him behind.

It’s Loaf he wants, because Loaf has the jewels.

Or maybe it’s the other way around—I have something Loaf doesn’t have. Something Vadesh fears. I have knowledge. I was trained by an expendable, and Loaf was not.

What did Father teach me that Vadesh should fear? Whatever it was, Rigg was not aware of it. Everything Rigg could remember had to do either with trapping animals and surviving in the wilderness, or the training in politics, economics, languages, and history that had enabled him to thrive in Aressa Sessamo. If nearly getting killed a dozen times could count as thriving.

And science. Father had taught him biology, physics, astronomy, engineering. As much as Rigg could absorb. Useless things that suddenly became useful when he was getting tested by leading scholars to determine whether he could have access to the library.

Useless things that suddenly became useful. But Father couldn’t have known that I would face such a board of examiners. Could he?

One thing Father did know, though, was that one day I would face another expendable. If every wallfold contained an expendable like Vadesh and Father himself, and if the jewels somehow allowed their owner to control the Walls and take them down, Father must have taught him what he needed to know to deal with the threat of someone like Vadesh.