That, and the sight of the fires on the eastern horizon, the mess around Arthur’s Seat that was visible from most of the city: this is real, and it’s coming this way.

Morag’s briefing, from the local authority emergency planners, had been rudimentary, but effective.

For instance, how to tackle looting. Looting was rare — bad guys flee too if the danger is real — but the fear of looting, whipped up by inaccurate reporting, was something you had to deal with. People wouldn’t have their houses marked as empty, for instance, for fear of making them targets. So you had to reassure. It was one reason she was still here now, a bobby on the beat in the empty heart of Edinburgh: to reassure the thousands who had gone.

The most heart-rending moments had been dealing with people who couldn’t move themselves. The elderly. The disabled. A team of interpreters had combed the Asian communities, to make sure the message got home there. Once Morag had found a house occupied by a deaf couple; she’d had to call out a sign language interpreter.

There were a lot of people on the margins. She’d never realized how many. Like the people dumped out of homes and hospitals under the Care in the Community programme. It had reduced the nation’s welfare bill, and no doubt done some kind of good in many cases. But, by God, it had added to the strain in this situation.

The gold police commander, the Chief Constable, had estimated that fifteen per cent of the population had needed direct attention and assistance of some kind. Fifteen per cent.

Anyhow, now it was done; as far as she could tell, George Street was empty of human life — empty, at any rate, of anybody who wanted to move.

She studied the eighteenth-century buildings that studded the street. There were two great churches, St George’s and St Andrew’s, the latter with its spire rising out of a Pantheon-like neoclassical building The monumental banks and insurance houses were a blizzard of porticos, pediments and pilasters. But this was no museum, but the heart of a working city; many of the buildings had modern frontages of glass and plastic grafted on to them, sometimes with a brutal lack of grace.

She reached the intersection of George Street with Frederick Street She stood at the feet of the statue of Thomas Chalmers, founder of the Scottish Free Church, and looked north. Monuments everywhere to the great men of the past, who had looked for immortality in stone and bronze.

Beyond a line of trees she saw blue sky, a hint of the waters of the Forth. The fresh light, still untainted in that direction by the smoke from Arthur’s Seat, drenched the prospect in loveliness.

It was so beautiful, the world was so beautiful, and she had seen so little of it.

Maybe she should go find her family, her mother and father. They had headed west out of the city; she knew where they should have got to by now.

But she still had her duty.

She turned away from the sunlit trees. She walked south, and turned into Princes Street, and continued to knock on doors.

A helicopter flapped over her head; she stared up to see its rotors glittering in the sun.

The Chinook set down in the centre of Princes Street Gardens. It was a crude chunk of military hardware in the middle of this Georgian garden, its runners crushing ornate flower-beds, the noise of its rotors clattering rudely from the elegant buildings.

Henry, clutching his petrological microscope, lumbered up to the chopper, looking for somewhere to sit.

The interior of the Army Air Corps Chinook was spartan, just a bare hull with plastic coating over the frame. There were no seats. There were soldiers here in field kit, a patrol on their way to some assignment of their own. The men were hot, sweating, sitting in the roar of the engines on a non-slip flooring littered with dirt. Their packs were strapped down to the floor, with cyalumes — lamps — around them. The men were rooting through the crew’s kit they found there, pinching chocolate bars and Coke with a practised thoroughness.

And I complained about British Airways, Henry thought. Well, there wasn’t a lot of choice. Maybe if he padded his jacket under his ass—

A loadmaster tapped him on the shoulder. “Not here, sir. You can ride upfront, in the cockpit.”

“Is that any more comfortable?”

The loadie shrugged. “The company’s better.”

So, with an effort, Henry climbed into the cockpit, and took a jump seat behind the pilot and copilot. The pilot was on the left — no, he was the guy on the right, damn it, these Brits took the wrong side of the highway even in the air. He nodded to Henry, a crisp “Sir’. The pilot seemed young, an NCO; Henry would have said he was working class if that hadn’t become, he’d learned, an outdated analysis of British society.

The cockpit was a cave of switches and dials and screens; the pilot and copilot were working through their take-off routine.

“Pedals in neutral.”

“Pedals.”

“Cyclic centred, collective lever down.”

“Got it.”

“Clear left and right.”

“Go for it.”

“Rotor brake off. Wind up rotors.”

“I got it…”

The noise of the rotors rose.

The Chinook lifted with a surge that made Henry’s stomach sink a little deeper inside his frame.

Thanks for the warning, fellas.

Edinburgh turned into a glowing map spread out beneath him, a folded blanket of green cut through by the blue of the Forth, the grey-black of the buildings, the lumpy outcrops of volcanic rock. The road network, clean and well-maintained, was a black thread like a kid’s toy track, its markings clear and bright. Today the roads were empty, save for a few scattered and stationary vehicles.

In the middle of the rectangular, oddly American grid that was the New Town, someone was standing, alone, looking up at him, face a bright white dot.

“One hundred feet… eighty feet…” the copilot said.

“Roger, eighty feet. Ninety knots.” The pilot turned, his eyes insectile behind big tinted goggles. “So you’re from NASA, sir?”

“Yup.”

“Always glad to give you Yanks a flying lesson. Staying at eighty feet, ninety knots.”

The Chinook dipped sharply to the right. Henry looked for a sick bag; there was nothing that qualified.

“This is a little slow for you, I suppose, sir.”

“I’m a scientist, not an astronaut.”

Now the Chinook was flying low over Arthur’s Seat.

The plug looked extraordinarily ugly from the air, a crude knot of basalt protruding from the ground, old and stubborn, somehow magnificent. Its several ancient vents were easy to make out, the basalt outline clear beneath a thin coating of heather. The Seat had, thought Henry, already seen off three hundred million years of weather, the titanic scraping of the ice, the pinprick depredations of man. But it wasn’t going to be able to see off the Moonseed. And there, indeed, close to the summit, was the central pool, obscured a little by the smoke from the ruin of Abbeyhill, shining like a coin in the ashen light.

And elsewhere, there were signs of magmatic activity: the blur of steam and smoke, perhaps a fissure near the crest of the Seat. He wished he had a cospec up here. A camera, even.

Incredibly, there were people on the Seat: still, even now, with the whole damn city evacuated, right at the heart of the thing.

Then, as the Chinook completed its second orbit of the Seat, Henry thought he spotted landsliding, on the south face, away from the ragged patches of Moonseed.

It was beginning.

He tapped the pilot on the shoulder. “Could you circle a few times? I’d like to take a closer look.”

“Surely, sir. Break my right now. That’s nice…”

The Chinook dipped to the right and hurled itself into a dive.

The copilot intoned, “Seventy feet, ninety knots. Sixty feet, one hundred knots.”