He expanded the scale of his graph. He would be able to figure out how far out this shit would reach, given time… It wasn’t reassuring. This was the easy part, of course. And he had already started to skew the work in the lab, focusing on this accelerating phenomenon, with studies of field samples, literature searches and phone calls to check on comparable cases (there were none). That was easy, too, all under his control, more or less.

The tough part was figuring out what the hell to do about this, how to tell people. From that, he found himself shying away. It wasn’t any part of his career plan to become a prophet of doom.

But if his numbers were right — if the phenomenon wasn’t self-limiting, if this inexorable growth continued — soon he wasn’t going to have a lot of choice.

Afterwards, Henry walked up the glacial tail of Castle Rock, towards the Castle grounds themselves.

The crest of the tail was topped by a chain of streets known collectively as the Royal Mile. The buildings here, the heart of the Old Town, were antiques, and some were imposing, like the uncompromising block of St Giles” Cathedral; and it was startling to see, peering through steep alleys, a glimpse of the blue waters of the Firth. But to Henry the place was polluted by twee tourist shops selling junk, kilts and bagpipes and whisky marmalade and Scottish ancestry gizmos.

But some of the pubs were good. And he had to admit he had paid his dollar to go see the Camera Obscura, a Victorian sight-seeing gimmick that worked better than he had expected.

Castle Rock was another volcanic plug, smaller than Arthur’s Seat but of the same vintage, sprouting from the same underground magmatic complex. The Castle itself was a sandstone mound of buildings, walls and turrets and battlements, looking as if it had grown out of the basaltic crag on which it was built.

He walked around the grounds, inspecting the basalt that underpinned the Castle — in some cases, rocky outcrops had simply been incorporated into the walls — but to Henry’s relief there was no sign here of the contamination which had disfigured the Seat.