That was when Father started teaching him about the way land changes with the climate and weather and growth of plants and all the other things that can shape it.

When Rigg was eleven, he had thought of a question of his own. “If wind and rain and water and ice and the growth of plants can chew up rock, why is Upsheer still so steep? It should have weathered down like all the other mountains.”

“Why do you think?” asked Father—a typical non-answer.

But this time Rigg had already half-formed his own theory. “Because Upsheer Cliff is much newer than any of the other mountains or hills.”

“Interesting thought. How new do you think it is? How long ago was this cliff formed?”

And then, for no reason at all that Rigg could think of, he made a connection and said, “Eleven thousand, one hundred ninety-one years.”

Father roared with laughter. “The calendar! You think that our calendar was dated from the formation of Upsheer Cliff?”

“Why not?” said Rigg. “Why else would we keep a memory that our calendar began in the year eleven-one-ninety-one?”

“But think, Rigg,” said Father. “If the calendar began with the cataclysm that could raise a cliff, then why wasn’t it simply numbered from then? Why did we give it a number like 11,191 and then count down?”

“I don’t know,” said Rigg. “Why?”

“Why do you think?”

“Because when the cliffs formed”—Rigg was not going to give up on his idea—“they knew that something else was going to happen 11,191 years later?”

“Well, we reached Year Zero when you were three. Did anything happen?”

“Lots of things happened,” said Rigg. “A whole year’s worth of things.”

“But anything worth remembering? Anything worth building your whole calendar around?”

“That doesn’t prove anything, Father, except that the people who invented the calendar were wrong about how long it would take to get to the thing they thought would happen in Year Zero. People are wrong all the time. It doesn’t prove that the calendar didn’t begin with the formation of Upsheer.”

“Good thinking,” said Father, “but, of course, wrong. And why are you wrong?”

“Because I don’t have enough information,” said Rigg. It was always because he didn’t have enough information.

“There’s never enough information,” said Father. “That’s the great tragedy of human knowledge. No matter how much we think we know, we can never predict the future.”

Yet there had been something in Father’s tone that Rigg didn’t trust. Or maybe he simply didn’t trust Father’s answer, and imagined he heard it in his tone.

“I think you know something,” said Rigg.

“I should hope so, as old as I am!”

“I think you know what was supposed to happen in Year Zero.”

“Calamity! Plague! The end of the world!”

“No,” said Rigg. “I mean the thing the calendar-makers were thinking of when they started in eleven-one-ninety-one.”

“And how would I know that?”

“I think you know what it was,” said Rigg, “and I think it actually happened, right on schedule.”

“And it was so big and important that nobody noticed it except me,” said Father.

“I think it was something scientific. Something astronomical. Something that scientists back then knew would happen, like planets lining up or some star in the sky blowing up or two stars crashing or something like that, only people who don’t know astronomy would never notice it.”

“Rigg,” said Father, “you’re so smart and so dumb at the same time that it almost takes my breath away.”

And that had been the end of that. Rigg knew Father knew something, and he also knew Father had no intention of telling him.

Maybe Nox would know what happened in Year Zero. Maybe Father told her all his secrets.

But to get to Nox, Rigg had to get down Upsheer to the village of Fall Ford. And to get down Upsheer, he had to reach Cliff Road, which was on the other side of the falls, and so he had to cross over the very place where the water ran fastest, the current strongest, and where he knew the boulders were being undermined and eaten away and it was quite possible that his step on one of the rocks would be the tipping point, and it would tumble over the falls and carry him down to his death.

And his consolation, all the way down, until the water or the rocks or just the force of landing pulverized him, would be that at least there’d be a big flood of water gushing out of the lake, so he wouldn’t die alone, the whole village of Fall Ford would be swept away in moments.

He remembered that this had been one of Father’s test questions. “Why would people build a village in a place where they know eventually there’ll be a terrible flood with no hope of survival and no warning in time to get away?”

“Because people forget,” Rigg answered Father.

“That’s right, Rigg. People forget. But you and I, Rigg—we don’t forget, do we?”

But Rigg knew that it wasn’t true. He couldn’t remember a lot of things.

He remembered the route across the rocks. But he didn’t trust that memory. He always checked it again when he got to the starting place, just above the surface of the lake.

It seemed so calm, but Rigg knew that if he dropped a stone it wouldn’t sink into the water, it would immediately be pushed toward the falls, moving as rapidly as if someone under the water had thrown it. If he dropped himself into the water, he, too, would be over the cliff in about two seconds—having been bashed into six or seven big rocks along the way, so that whatever fell down the waterfall would be a bloody bashed-up version of Rigg, probably in several pieces.

He stood and looked out over the water, seeing—feeling—the paths of countless travelers.

It wasn’t like a main road, which was so thick with paths that Rigg could only pick out an individual with great difficulty, and even then he would lose the path almost at once.

Here, there were only hundreds, not thousands or millions of paths.

And a disturbing number of them did not make it all the way across. They got to this spot or that, and then suddenly lurched toward the cliff face; they had to have been swept away by the water.

Then, of course, there were the ancient paths. This is why Rigg had been able to figure out about the erosion of the rock, the way the falls moved back and lower over time. Because Rigg could see paths that walked through the air, higher than the falls and fathoms outward. These paths jogged and lurched the way the current paths did, for the people who made those paths had been crossing on another set of rocks that penned in a higher, deeper lake.

And where the bridges used to be, thousands of ancient, fading paths sweeping smoothly through midair.

Of course the land had moved, the water had lowered. Someone who could see what Rigg could see was bound to figure out that the falls kept moving.

But today, here is where they were, and these rocks were the rocks that Rigg would have to cross.

He always chose a route that almost everyone had crossed safely; he always tried for a route that was well back from the edge.

Rigg remembered—or remembered Father telling him about it, which was as close to memory as didn’t matter—how Father had first discovered Rigg’s ability to find old paths, right here at the footcrossing of the water. Father had been about to leap, carrying little Rigg, from one stone to another, and Rigg shouted, “No!” He made Father take a different path because, as Father told him, “You said, ‘Nobody fell into the water this other way.’”

Rigg saw now the thing he saw then: Paths from stone to stone, different people, days or years or decades apart. He saw which of the paths of fallers were old and which were new. He chose a route that looked dry, that had been used most recently.

He saw his own past paths, of course.

And, of course, he saw no path at all belonging to Father.