The door opened, as if automatically, and some kind of butler let him into a pretty impressive hallway. The butler was a big, balding, well-muscled guy. A plain clothes cop, no doubt.

A young suited man shook Henry’s hand. “Dr Meacher? My name’s Pearson. I’m the Prime Minister’s PPS — uh, political secretary.”

“The Prime Minister?”

“Didn’t you know you were seeing him? He’s waiting for you upstairs in his study. I’ll tell him you’re here.”

The aide ran off up the narrow staircase. Henry was left standing with the Bruce Willis butler.

It was just a smart old town house, on the surface. But Henry knew there was more to it than met the eye. For instance there were corridors that led to the other houses in the row, such as Number Eleven, the residence of the Chancellor of the Exchequer, the finance minister. So, behind the facade, this was all one big house, like the Beatles” shared home in Help!; he half-expected to see John Lennon playing a Wurlitzer come ascending from the floor.

It was hard to believe you could run a modern country from such a place, but evidently the Brits managed.

“So this is Number Ten,” he said to Bruce Willis.

“How true, sir.”

“It seems kind of — poky. What’s that big place down the corridor? The pool room?”

“We call it the Cabinet Room, sir.”

The political secretary returned, and escorted him up the stairs. The walls were lined with portraits of what looked like previous Prime Ministers. Henry recognized some: Churchill, Thatcher, Major, Blair, Portillo.

The Prime Minister was standing in front of the window.

Over the PM’s grey-suited shoulder was a hell of a view, of what looked like Horse Guards Parade. A couple of other people — a man and a woman, both sweating in heavy suits — were sitting in hard-backed chairs before the desk. The desk itself was a mess; its green leather top was covered by loose papers and scribbled notes and a big map of Britain. There were plates of abandoned sandwiches on the window sill, and a half-drunk bottle of red wine and three glasses leaving stains on the desk. It looked as if meetings had been going on here through the night.

The Prime Minister turned and came forward. He looked tired, his face slack, his thick hair greyer than Henry remembered from TV. “I’m Bob Fames,” he said. “Dr Meacher, thank you for coming.”

“It’s, umm, an honour.”

Fames introduced the others. The man, so fat his belly strained the buttons of his off-white shirt, was called Dave Holland, and he was the environment minister. The woman, a thin, intense Asian, was called Indira Bhide. Her title was Home Secretary, which meant, as Henry understood it, she was the most senior interior minister.

Fames said, “We have projections from our own science advisers. But Professor McDiarmid tells us you’re the best qualified to brief us on this phenomenon.”

Henry wasn’t expecting that. Was McDiarmid uncharacteristically avoiding the credit for Henry’s work on the Moonseed — or, more likely, trying to avoid the heavy shit?

“Tell us what we’re dealing with here, Dr Meacher,” Fames said. Henry spread his hands and summarized what he’d found out about the Moonseed. “It eats rock. It prefers igneous rocks — basalt, for instance. Volcanic rocks. It is spreading across surface rock, subsurface rock, and down into the mantle. Also, after the Arthur’s Seat incident, it is also spreading through the mantle itself, and through the stratosphere in the form of dust.”

“I’m told it slowed down, after the Edinburgh eruption.”

“Yes. I expected that.”

“You did?”

“It doesn’t just grow. It builds things. Structures in the rock. Now it’s into the deeper rock, we think it is busy building. But its spread will resume.”

Holland pulled his lip. “So you say.”

“Yes.”

“Not everyone agrees with you.”

He’d been expecting that. “They haven’t had time to study it the way I have.”

They were staring at him, their faces grave — Christ, they’d already lost a city, they’d already presided over Britain’s biggest peacetime disaster — but, even so, not grave enough.

He turned to the desk, and pulled the Britain map towards him. “Look. Here’s Edinburgh, Right now, we think the outbreak is around two months old, and it’s maybe four miles across. In another couple of months it will be out as far as here.” He stabbed at a point twenty miles to the east of Edinburgh. “What’s this? Some kind of nuclear plant?”

“Torness,” said Bhide quietly.

“Okay. A few weeks after that, it will reach here.” An urban sprawl at the western end of the Midland Valley, Glasgow. “And you won’t get the slow burn you had in Edinburgh. It will sweep over the city in a day.” He studied them. “Somewhere about then, it’s going to be moving faster than most people can walk. After that it will dig through the crust and—”

“Dear God,” said Holland. “What about the rest of Britain? North England — even London—”

Henry shrugged. “The projections are chancy. And we have to expect more incidents as it eats into old magmatic structures — dead volcanoes, weaknesses in the crust — and, given time, the Moonseed will attack the crust itself. The ocean floor is about five miles thick; the Moonseed will take a few weeks to get through that and down to the asthenosphere. The continental crust is more like fifty miles thick—”

“What happens then?”

Henry looked for the right expressions. “The scale of the irruptions is going to increase.”

“Beyond anything we’ve yet seen?”

“Beyond anything in recorded history.”

Fames withdrew to his window, and the sunlight streaming in there silhouetted him, masking even his posture.

Holland said briskly, “So how can we stop this thing?”

“We don’t know. We’re trying to find a way. It can be inhibited. The Moonseed has to form, umm, certain crystalline structures before it can spread effectively. If you disrupt those structures, we think it can be slowed down.”

Holland looked confused. “What do you mean, disrupt?”

“Mechanically. Break it up. Bomb it.”

“Nuclear weapons? We couldn’t sanction—”

“No,” said Henry firmly. “The radiation from a nuke would probably feed it more than inhibit it. Carpet-bomb the infection sites with conventional weapons. Water helps.”

“Water?”

“Under high pressure. Flood it wherever you can. The earlier you can catch a new infection site the better your chance of disrupting its growth, we think.”

“You think?” snapped Holland. “Damn it, man, don’t you know?”

“No, sir, I don’t. At Edinburgh we did some lab tests but we didn’t have time to test any of this in the field.”

“But at least we can slow it down.”

“I think so. You can buy some time.”

Holland said, “What about further afield? Beyond the sea. Ireland, the continent—”

“We think it will be inhibited by the ocean. The Moonseed likes dry rocks and sunlight. But it will migrate eventually, even if it has to go through the mantle.”

“Evacuation,” Bhide said. “That’s what we’re looking at, if Dr Meacher is right. First the Scottish Midland Valley towns. We can send people to the highlands and islands in the far north, to northern England, and out of Britain altogether. To Northern Ireland. Eire. France.”

“We’ll have to think about the royals,” Fames said abruptly. “Get them to Canada maybe. Christ. The bloody royals. The King will hate it; he despises the Canadians…”

Holland stepped forward, angry. “Oh, this is all rot. Do you have any idea what you’re talking about?” he snapped at Bhide, and Henry saw old rivalries tense between them. “These are all short-term palliatives. If this gentleman is right, inside a few months, we would have to evacuate the country. It’s impossible. The capacity of the airports, the sea ports, the Channel Tunnel… Dr Meacher, we’re talking about moving sixty million people.”