“I told you. I think Willis keeps me.” He poured her more tea. “We have a partnership of equals, me and that animal.”

“Where is he now?”

He eyed her. “Not here.”

The house shuddered gently.

Concentric ripples on the meniscus of her tea, like a tube tram passing far beneath the foundations. Except there was no metro in Edinburgh. Or maybe like a heavy lorry rolling by, shaking the ground.

But Viewcraig Street was a cul-de-sac.

She glanced up at Ted. He was watching her carefully.

“Funny weather,” he said.

“Yeah.”

“Listen, do you have a couple of minutes? There’s something I’d like you to take a look at.”

They walked out to the back of Ted’s house, towards Arthur’s Seat. They headed up the slope towards St Anthony’s Chapel. Soon they were off the path and climbing over a rising rocky slope; the grass slithered under Morag’s polished shoes. Once they’d risen twenty yards or so above the level of the road, the Edinburgh wind started to cut into her.

“I’m not equipped for a hike,” she said.

“You’ll be fine.” Ted’s grizzled pillar of a head protruded from the neck of his thick all-weather rad-proof jacket. His legs worked steadily, hard and mechanical, and his breath was deep, calm and controlled.

It was quiet, she noticed absently. There was the moan of the wind through the grass, the distant wash of traffic noise from the city. But that was about all.

What was missing?

She stopped. “Bird song,” she said.

“What?”

“I can’t hear any bird song. Can you? That’s why it’s so quiet.”

He nodded, and walked steadily on.

A few dozen yards further, Ted halted. He pointed up the slope, towards the grey, brooding pile of the Chapel, where it sheltered under the crag, still a couple of hundred yards away. “There,” he said. “What do you make of that?”

“What?”

“Don’t they teach you observation any more? Look, girl.”

She looked, and stepped forward a couple more paces.

Under scattered fragments of broken orange-brown igneous rock, under green scraps of grass and heather and moss, there was a silvery pool. It clung to the outline of the crag, as if the rock had been painted.

“Now,” said Ted, “this used to be solid rock. I wouldn’t step much further.”

“Why not?”

He bent and picked up a chunk of loose rock. With a reasonably lithe movement he threw it ahead of her, into the dust.

It sank out of sight, immediately, as if falling into a pond.

“Wow,” she said. “How far does this go?”

“I don’t know. There seem to be other pools, up around the summit, and then the odd outbreak like this one. Like something coming through the rock, somehow.”

“Has anybody been hurt up here?”

“Sunk in the dust, you mean? Nothing’s been reported, so far as I know.”