The Chinook lurched; the pilots fought for control.

There was an explosion nearby: a crackle of acoustic shock waves, a blast of light, as if someone was shooting at the chopper.

“What—”

“Hold on!”

The Chinook rocked violently.

“Break left! Break right!”

The Chinook banked; Henry grabbed the frame, but even so he was thrown from side to side.

Thick and viscous magma, he thought. Undisturbed for three hundred million years. Heavy with dissolved gases. Suddenly the Moonseed takes the lid off. The magma tears itself into hot fragments, that jet upward or tear out of the new/old vent. Hurling volcanic bombs into the air, even high enough to threaten this Chinook.

Understanding it, he found, was no reassurance right now.

The rocking began to reduce.

“Take it easy,” the pilot said.

The Chinook levelled out.

Henry looked back again. The cloud was still expanding faster than they could run, probably three hundred miles an hour or better, close enough now to turn the day dark.

There was a patter of ash particles on the windscreen.

“North,” he said. “Go north.”

The pilots hurled the Chinook into a sickening wrench to the left.

Henry looked back. The cloud was still expanding, but mostly southward; the north was shielded a little by the topography of the Seat, what was left of it.

The cloud was separating into distinct mushroom-shaped clouds, thick and black, heavy and pregnant with ash. There were lighter cirrus clouds arrayed above. He could see the ashfall beginning already, a black ram; it would turn what was left of Edinburgh into a new Pompeii, he thought.

The Salisbury Crags, at the western face of the Seat, had given way. He could see what looked like a pyroclastic flow, a heavier-than-air mix of gases and hot volcanic fragments. From here it looked like a smoke ring spreading down the battered western flank of the Seat. The flow would follow the contours of the ground, and pool in the lower areas: the heart of Edinburgh, the old loch that had been drained to build the New Town.

Already the Seat itself, what was left of it, was scraped bare of life. And, through the clouds, he couldn’t see any sign of the Moonseed pools.

Lightning bolts shot through the clouds, extending to tens of thousands of feet.

For Morag, it started with a low rumble, like a tram deep underground. But there were no trains running today.

Then a series of buffeting jolts. Jolts that grew stronger.

She stood in the middle of Princes Street, in the roadway away from the buildings.

Then she was down, her face slammed against the tarmac. It was as if a rug had been pulled away from beneath her feet.

She tried to get to her knees. There was blood on the tarmac, a deep sting down the right side of her face, where the skin had been scraped away.