She looked dubious. “I’m surprised they let you bring that thing in here.”

He looked at the microscope, through her eyes. It was kind of battered, he admitted. He’d picked it up for twenty bucks as an honours student when his department had a clear-out, and it had been old even then. But the mechanism still ran sweet as a nut, and the Swiss optics were as bright and clear as the day they were ground, and the “scope, worn smooth with use, had been all over the world with him.

Henry expected to be buried with his “scope.

Still, Mike had banned him from bringing its wooden box in here, which was even more disreputable.

He stepped forward to check the alignment. The view through the eyepiece was a disc of multicolored light, irregular shapes of bright colour. He twisted the analyser disc to show up the colours.

“Take a look,” he said. “Try to keep both your eyes open. After a while, you won’t see anything through your other eye.”

She bent, and turned the analyser as he showed her.

“What do you see?”

“It’s like a view down a kaleidoscope.” Jane straightened up. “Wow. I’m dizzy.”

“That’s your other eye cutting in. Forget it. The point of the “scope is that you can see what minerals are present there, just by letting the thin slice filter polarized light.”

“Just like that? At a glance?”

“At a glance. Neat, isn’t it?”

“What am I looking at? Your bedrock?”

“No That’s a reference sample. A lunar basalt from another suite, closer to the norm of the Apollo samples. Tell me what you see.”

She bent again. “Lots of small shapes, like a tiled floor. And, here and there, like pieces of stained glass window, rough discs and rectangles. Much larger shapes. Ships of glass, sailing among ice floes. As seen when on acid.”

He laughed. “What you’re looking at is a felted matrix of small elongate crystals of feldspar — that’s the grey stuff — pyroxene, yellow — and olivine, all the bright colours you can see, scarlet and yellow and pink and blue. And stuck in the matrix you have those bigger crystals, phenocrysts of pyroxene and olivine.

“Now.” He took out the slide, replaced it with another. “This is 86047. The bedrock. See if you can tell the difference.”

She looked.

“No olivine.”

“To a first approximation, yes.”

She straightened up, frowning. “So what?”

He lifted his white hat and ran a hand through his hair. “So, that’s wrong. I can’t figure out what process has taken out the olivine here.

“Look — rock is made of silicon and oxygen, and other stuff. The basic structure formed by silicon and oxygen atoms is a tetrahedron. An olivine molecule is built around a single tetrahedron, with iron and magnesium atoms stuck on. So olivine is the most basic form, the mother of all silicates.

“Deep in the mantle, at high enough temperatures, olivine is all you find.

“But when a lump of mantle material rises and cools, more complex molecules can form. You put together the tetrahedra like building blocks. First you get pyroxene, which has single chains of tetrahedra, then amphibole, which has double chains, and then mica—”

“I’ve seen mica. Flaky stuff, thin, papery sheets that you can chip off with a fingernail.”

“Right. Mica is made up of sheets of the tetrahedra. But then, when the mica cools further, you have quartz. A three-dimensional lattice, a tough, hard crystal. So you are getting more and more complex silica structures, built of tetrahedra.”

“So what happened here?”

“I don’t know. It looks as if something has — accelerated the process, in this lump of Moon rock. Reworked the crystalline structure.”

“Reworked? How?”

“I’ve no idea. One tack we’re following is trying to replicate lunar mantle processes in the high-pressure labs.”

In these, he told her, you placed a small sample of your rock in a foot-high stainless-steel block called a bomb, and then pressurized it hydraulically, as far as twenty thousand atmospheres, which corresponded to pressures in the Earth’s mantle.

Sometimes the bombs failed, and lived up to their names. So the labs were run remotely, and had steel plates built into their walls, and blast chimneys.

But the high-pressure tests weren’t showing them anything they didn’t know already.

“In the meantime, we’re ordering up other studies. X-ray fluorescence work, and time on the ion microprobe they have here. That lets us study the composition of very small samples of the rock…” He scratched his head under his hat. “I’ll tell you something else odd. The samples I’ve been taking from the liquefaction patch, on Arthur’s Seat—”

“I’d like my bottle back sometime.”

“Yeah. I ran them through the “scope, and a couple of other tests. They are deficient in olivine as well…”

She frowned.

“I can’t see any connection either. Spooky coincidence, huh.”

But she was hesitating. As if there was something, some connection, she wasn’t telling him.

He said, “You know, if this — whatever — is consuming olivine—”

“What?”

“The Earth contains a lot of olivine, in the mantle. No wonder that patch is growing. And it isn’t going to stop eating either.”

“Eating?” She laughed, a little nervously. “You make it sound alive.”

“I don’t know what the hell I mean.”

“Do you think we should tell somebody about this?” she asked.

“Like who?”

She shrugged. “The police.”

He blinked. That hadn’t occurred to him, that aspect of the situation. The threat. Maybe Geena was right that he had a one-dimensional mind.

“You know, I don’t like the inexplicable.”

“Oh, come on,” she said. “Be honest with yourself. I know you people. You have a puzzle, and that makes you happy. Something you have to figure out.”

He straightened up. “Buy me lunch and we’ll discuss it.”

She smiled.

“Listen, you want to see 86047 before you go? The bedrock sample. It’s in the case over there by the wall.”

She shrugged. “You’ve seen one Moon rock, you’ve seen them all.”

They made their way to the door, and squeezed into the improvised airlock together.

Behind them, in the central glove box, sample 86047 sat in the lab’s fluorescent light.

It had already been sliced in half and thin samples taken, by Houston technicians and Mike’s careful hands. In the harsh illumination it would have been difficult to tell for sure, but perhaps a careful observer might have noticed something odd about its flat, new surfaces, exposed for the first time since the formation of the rock, billions of years before.

The surfaces were glowing, softly silver.

And, with a rustle rendered inaudible by the layers of glass encasing the rock, a rain of fragments was whispering down from the exposed face.

Jane drove Henry to a multistorey car park close to Waverley Station, and they walked along Princes Street.

You could still make out the deliberate design of the old streets here, Henry thought: a neat rectangular grid pattern, almost like a US city. But whatever character the street had once had was pretty much obscured by the encrustation of plastic and glass of the modern department stores and fast food outlets. There was even a McDonald’s and a Dunkin” Donuts.

“This is what we call the New Town,” Jane said.

“I know. 1760. You told me.”

“The Old Town is the medieval town that grew up around Castle Rock. Narrow, windy streets, coming down the glacial tail there…”

“You’ve been building this city for a thousand years, on top of an extinct volcano. I think you people are seriously crazy.”

“Well, maybe. In the Old Town they burned witches; in the New Town they bred lawyers and scientists.”

“Split personality.”

“Yeah. Jekyll and Hyde.”

“Right. Didn’t Stevenson come from Edinburgh?”

“Yes. Maybe we do have a split personality,” she said. “It was in Edinburgh that the crucial moments in the Act of Union were played out. Union with England.”