“It took time for a strain of facemasks to develop that could thrive on the human body. So at first it was like a pesky fungal infection.”

“And then it wasn’t,” said Rigg. “Facemasks are that adaptable?”

“It’s not blind adaptation,” said Vadesh. “They’re a clever, fascinating little creature, not exactly intelligent, but not completely stupid, either.”

For the first time, it occurred to Rigg that Vadesh was not just fascinated by the facemasks, but enamored of them.

“They can only attach to their host in the water,” said Vadesh, answering a question no one had asked. “And once they attach to an air-breather, they lose the ability to breathe in water. They only get their oxygen from the blood. You know what oxygen is?”

“The breathable part of air,” said Umbo impatiently. Olivenko chuckled. Of course, thought Rigg—Olivenko was a scholar, and Umbo had studied for a time with Rigg’s father.

But Rigg noticed that Loaf and Param seemed to have no idea what Vadesh meant. How could air be divided in parts? Rigg remembered asking Father exactly that question. But there was no point in explaining the point now or soon or, probably, ever. Why would a soldier-turned-innkeeper and a royal heiress who had fled her throne require a knowledge of the elements, of the behavior of gases and fluids?

Then again, Rigg had thought, all through his years of education, tramping with Father through the woods, that he would never need anything Father taught him except how to trap, dress, and skin their prey. Only when Father’s death sent Rigg out in the world did he learn why Father had trained him in languages, economics, finance, law, and so many other subjects, all of which had proven vital to his survival.

So Rigg started to explain that invisible air was really made of tiny particles of several different types. Loaf looked skeptical and Param bored, and Rigg decided that their education wasn’t his job.

He fell silent and thought about parasites that could only attach to humans in water, and then they lost the ability to breathe on their own. Rigg filed the information away in his mind, the way Father had taught him to do with all seemingly useless information, so he could recall it whenever Father decided to test him.

I’ve been on my own for a year, thought Rigg, and still in my thoughts he’s always there, my pretended father, my kidnapper for all I know. He’s the puppeteer who, even dead, is pulling all the strings inside my mind.

Lost in such thoughts, Rigg did not notice the first building that came in sight. It was Loaf, ever alert as a soldier should be, who saw the glint of metal. “It’s like the Tower of O,” he said.

It was indeed, in that it was tall and of a similar substance. But it did not rise to a point and was not rounded like a cylinder. And there were several of them nearby, and none of them was half so tall as the Tower of O.

But they were impressive nonetheless, and tall enough that it took two more hours of walking after they first saw them for their little group to come close enough to see that these towers were made from the same material, and formed the skyline of a city.

“How could they build with this . . . substance?” asked Loaf. “People have tried to cut into the Tower of O many times over the years, and neither tool nor fire can affect it.”

“Who would try to damage it?” asked Umbo.

“Conquerors who want to show their power,” said Olivenko. “Rigg’s and Param’s people arose only lately. The Tower has been there ten thousand years.”

The talk of duration made Rigg realize something he should have noticed at once, as soon as they knew it was a city they were coming to. There were human paths again, as there had not been near the stream, but all of them were old. None more recent than ten thousand years.

“How long has this city been abandoned?” asked Rigg.

“It isn’t abandoned,” said Vadesh.

“There hasn’t been a human being here for a long time,” said Rigg.

“But I’ve been here,” said Vadesh.

You’re not a human being, Rigg wanted to say. You’re a machine; you leave no path. A place that contains only you is uninhabited. But it seemed too rude to say aloud. Rigg saw the absurdity of his attitude: If he truly thought of Vadesh as only a machine, rudeness would not be an issue.

“Where did the people go?” asked Param.

“People come and go in the world, and where there once were cities there are only ruins, and where once there was nothing, cities rise,” said Vadesh.

Rigg noticed how nonresponsive Vadesh’s answer was, but did not challenge him. Rigg trusted Vadesh too little to want him to know he wasn’t trusted.

“And there’s water here?” asked Loaf. “Because my need for it is getting pretty urgent.”

“I thought you field soldiers drank your own piss,” said Olivenko.

“We do pee into canteens,” said Loaf. “But only so we can bring it back for the officers of the city guard to drink.”

It could have been a quarrel, but to Rigg’s relief, Olivenko just smiled and Umbo laughed and it went nowhere. Why did they still irritate each other so much, after all they had been through together? When would rivals become comrades?

So all the people of this city were gone. Rigg began to scan for the paths that would show a great migration out of the city, but before he could make much progress, Vadesh led them into a low building of ordinary stone, which showed its many centuries of weathering.

“Did someone live here?” asked Umbo.

“It’s a factory,” said Vadesh.

“Where did all the people sit to work?” asked Olivenko.

“A mechanical factory,” said Vadesh. “And most of it is underground. I still use it, when I need any of the things the factory makes. But they needed safe water for the supervisors and mechanics, and for the people who hauled things in and hauled things out.” He led them through a doorway into a dark chamber. As they passed through the door after him, a bright light came from above. The whole ceiling was aglow, very much like the lights inside the Tower of O.

The others gasped in awe, but Rigg was noticing that the paths of humans into this chamber were few and ancient. This building had only been used for a few decades at the most. It had been abandoned by the same generation of people who had built it.

Vadesh touched the front of a thick stone pillar and at once they heard the sound of running water inside the pillar. Then he touched another place, and a portion of the pillar came away in his hand. It was a stone vessel halfway between a drinking mug and a waterbucket in size. He handed it to Loaf. “Because your need was so urgent,” said Vadesh.

“Is it safe?” asked Rigg.

“It’s filtered through stone. No parasites of any kind can possibly get into this water.”

Again, Rigg noticed that while Vadesh answered, he only answered about the likelihood of parasite infestation, not the actual question Rigg had asked.

Loaf handed the water to Param without tasting it. “You need this most,” he said.

“Because I’m a frail princess?” Param asked with a hint of resentment.

Well, she was physically frail and she was a princess. Until their mother tried to kill her and Rigg, she was assumed to be heir to the Tent of Light. Years of living in the narrow bounds of captivity had made her physically weak, and the journey to the Wall had only improved her stamina by a little. But no one was rude enough to point this out to her.

“You need it most because you and Umbo lived on your water for an extra week that we didn’t live through,” said Loaf.

Param took the water and drank. “It’s perfect,” she said. “It tastes fresh, and nothing else. Except a tinge of something . . .”

“Trace metals,” said Vadesh. “From the rock it filtered through.”

Umbo drank next. He tried to pass it to Rigg, but Rigg would not take any until Loaf and Olivenko had also drunk.