“And we can’t be the first to figure it out if it is,” said Rigg. “Why haven’t we heard about this?”

“Well, we have,” said Loaf. “I have, I mean. Why do you think the pilgrims say, ‘The Tower of O lets you see the whole world’?”

“I thought they meant you could see really far from the top of it,” said Umbo.

“But they also say, ‘All of the world is inside the tower,’” said Loaf.

“I thought that was mystical booshwa,” said Rigg. “Or maybe just talking about how many pilgrims come here.”

“It’s weird to think of the world that way. Very disturbing. I mean, the world is the land inside the Wall—that’s what the word means. How can there be more of the world than the whole world itself? How could anybody know what’s outside the world?”

Rigg had been counting. “There are nineteen of them—nineteen lands surrounded by yellow lines. And quite a bit of land that isn’t inside any of the yellow lines.”

“So there are nineteen worlds on this same globe?” asked Loaf. “Is that what the Tower of O is saying?”

“No wonder people don’t talk about it after coming here,” said Umbo. “It’s just too crazy. Even if they think of it this way—and Rigg’s father was no fool and no liar, either, so if he says that we live on the surface of a ball, it’s probably true. Somehow. Even if they think of this as a map of nineteen worlds on the face of a globe, who’s going to believe them? People would think they were crazy.”

“I think you’re crazy,” said Loaf. “Except the map of the world—of our world—is accurate enough. The military keeps maps like that—all the world inside the walls, all the roads and towns. It’s illegal for anyone else to make them, though. So I wonder how you knew it was a map, Umbo.”

“Our schoolteacher showed us a map. Smaller than this, but it had the river on it, and Aressa Sessamo at the mouth of it, and the big bay. And the line of the Wall.”

“It was against the law for the schoolteacher to have a map like that,” said Loaf.

“Oh, he drew it himself, I think. On a slab of wood. With chalk. And . . . then he went away.”

“How long after he showed you that map?” asked Loaf.

“I don’t know. After. He only showed it to us the once.”

Rigg had been scanning the walls while he listened. “There are nineteen pillars of stone holding up the walls. Nineteen ribs to the tower. A map with nineteen lands surrounded by walls. Nineteen isn’t a convenient number to work with mathematically. To divide the circle of the tower by nineteen—that’s just crazy, unless they were doing it to have the same number as the number of lands.”

“Do you think if these really are other wallfolds,” said Umbo, “there might be people in them?”

“There are red dots and white dots and blue dots in all of them,” said Rigg.

“Boys,” said Loaf, “you have no idea how illegal this conversation is.”

“You’ve been to the Wall,” said Rigg. “Were there people on the other side?”

“Nobody goes right up to the Wall,” said Loaf. “The closer you get, the more fearful and sad and desperate you get. You have to get away. You’d go crazy if you didn’t. Nobody gets close. Even animals stay away—on both sides.”

“So you only saw it from a distance?” asked Rigg.

“We patrol the edge, because that’s where a lot of criminals and traitors and rebels like to go—close enough to the Wall that other people stay away, but not so close they actually go crazy. In a way, it’s a fitting punishment for them, living with the dread and grief and despair. But it was our job to go into the zone of pain and force them out. So they wouldn’t keep coming out and foraging or raiding or recruiting.”

“If it’s the same way on the other side,” said Rigg, “then even if there are people there, they won’t come any nearer the Wall than you did. So they wouldn’t see anybody on our side and we wouldn’t see anybody on theirs.”

Loaf drew them closer, his hands tight on their shoulders. “You’ve been talking way too loud. Now I think I know why your future self came back to warn us.”

“No,” said Umbo. “If we got arrested for talking, I would have told myself and Rigg to just shut up.”

“Well, I’m telling you to do that,” said Loaf. “Your teacher probably came here and thought about what he saw and memorized the map as best he could. I’m betting that’s what happened. Because any soldier—well, any sergeant or higher officer—might recognize this map for what it is, if he happened to come to this side of the sphere. And then he might memorize it. But soldiers would know to keep their mouths shut. And never, ever to draw an unauthorized copy.”

“Why not?” asked Umbo.

“Because,” said Rigg, putting things together the way Father had taught him, “the army doesn’t want any of its enemies to have an accurate map of the world.”

“Exactly,” said Loaf. “Now let’s get out of here before somebody notices us lingering so long looking at the globe.”

But Rigg would not leave, not yet. He looked at the maps of the other eighteen wallfolds and tried to imagine the cities. In one, the wallfold just to the north of the one they lived in, the cities were out on the blue part, even though the blue had to be the ocean and the rivers that feed into it. The blue covered more of the globe than Rigg had imagined possible, though Father had told him there was more ocean than land in the world. It never crossed his mind to wonder how Father could know such a thing. Father knew everything, Rigg took that for granted, but now he had to ask himself, how could Father have known how much ocean there was in the world, when you couldn’t get through the Wall?

Father has been through the Wall.

No, thought Rigg. Father merely came here to the Tower of O and reached the same conclusion we did.

But someone must have been through the Wall, or this map could never have been made.

Until today Rigg had never even worried about the Wall. He knew it was there, everybody knew it was there, and so what? It was the edge of the wallfold, which meant it was the edge of the world. You didn’t even think about it. But now, in this moment, knowing that there were eighteen other wallfolds, all of them surrounded by an invisible Wall, Rigg longed to get to one of the other wallfolds and see who lived there and what they were like.

And the only thing blocking him was an invisible Wall, one that supposedly drove you crazy if you got too near. But you could see through it. You should be able to walk through and get to the other side.

At last Rigg gave in to Loaf’s prodding, and they set out on the downward ramp. “I’m going to go to the Wall,” said Rigg softly.

“No you’re not,” said Loaf. “Unless you’re a criminal or a rebel, and then it will be the job of somebody like me to hunt you down and kill you.”

“I’m going to go there and see the paths,” said Rigg. “If anybody ever crossed the Wall, I’ll be able to see where. And if I have you with me, Umbo, I’ll be able to go back and ask them how they’re going to do it. How it’s done. Just before they cross I’ll ask them.”

“Unless it was somebody like your father,” said Umbo, “who made no path.”

“True. If Father crossed I wouldn’t know it.”

“Or anybody like your father.”

“There’s nobody like my father,” said Rigg.

“That you know of,” said Umbo. “Because if there were others before him who left no path, you wouldn’t know about them.”

“That’s kind of an important hole in your talent, there, Rigg,” said Loaf. “That’s like saying, ‘We have a spy network that sees all our enemies . . . except the ones we can’t see.’ How sound do you think that sergeant will sleep at night?”

“There could be hundreds like your father,” said Umbo.

“Father wasn’t invisible,” said Rigg. “If we had ever run into somebody else without a path, I would have known it.”

“But you never saw many people,” said Umbo. “You just went out into the woods and then came to Fall Ford and how many other villages did you even visit?”