They walked on for a time. The path ascended and descended, a gentle switchback, as the lava sill waxed and waned in thickness.

At the end of the sill, they clambered up a steep, eroded path towards the summit of Arthur’s Seat.

At the summit, they sat on broad, worn-smooth patches of ancient agglomerate. Henry found the backs of his legs were aching pleasurably; he hadn’t been getting enough exercise, he realized.

They looked to north and west, over the city. A blue mist, sharply defined, lay across the land. The spires and towers of the city poked out of the mist. A waning Moon, thin and attenuated, hung in the sky.

“The old folk call the mist the haars,” Jane said.

“It’s beautiful.”

“On a clear day you can see a long way. All the way across the Midland Valley graben from the Highlands, fifty miles or so to the north, and down to the Southern Uplands, ten miles south-east of here, beyond the coal field—”

“I’m impressed.”

“By the view?”

“By the fact that you know terms like graben.”

“You’re such a patronizing arsehole.” But this time her tone was so mild it almost sounded affectionate.

“Thank you,” he said. “So what about you? How did you get into, uh, rocks?”

“And all the other cookie-girl New Age stuff, you mean?”

“I didn’t say that.”

She pulled at a tuft of grass. “Actually, it was the Moon.”

“The Moon?”

“I read a science fiction story which shocked me. I was only ten or so — about Jack’s age, I guess.”

“What story?”

“I don’t remember the title. I think it was a Heinlein. The point was, he suggested the Moon is the way it is because of a nuclear war up there. It blasted off the atmosphere, and boiled the oceans, and killed everybody.”

He nodded. “And Tycho was just the biggest arms dump.”

“You know it. You don’t need to tell me it makes no sense.”

“I wasn’t going to.”

“It scared me to death. As I got older I started to read about all the perils we faced — still do face. Before I left school I was organizing recycling drives. I read politics and economics at university. I got into real politics later, mainly with the Greens. Not that I ever got elected anywhere. But that doesn’t pay the bills—”

“Hence the rock shop.”

“Yeah.”

“So,” he said. “You’re what we’d call a survivalist? You think that when it all falls apart we should pack up and head for the hills?”

“No.” Now she did sound offended. “Of course not. We’re human beings. We got where we are by cooperating, by helping each other. It’s just that the future is so dangerous.”

“Yep.”