“You know, you look like Beethoven,” she told him thoughtfully, as the camera closed in on a marble bust of the composer.

“With a buggered nose,” said Strike. He had been told it before.

“And why are you going to Scotland?” Elin had asked as he reattached his prosthetic leg while sitting on the bed in her bedroom, which was decorated in creams and whites and yet had none of the depressing austerity of Ilsa and Nick’s spare room.

“Following a lead,” said Strike, fully aware that he was overstating the case. There was nothing except his own suspicions to connect Donald Laing and Noel Brockbank to the severed leg. Nevertheless, and much though he might silently lament the nearly three hundred quid the round-trip was costing him, he did not regret the decision to go.

Grinding the stub of his cigarette under the heel of his prosthetic foot, he proceeded into the station, bought himself a bag of food at the supermarket and clambered onto the overnight train.

The single berth, with its fold-down sink and its narrow bunk, might be tiny, but his army career had taken him to far more uncomfortable places. He was pleased to find that the bed could just accommodate his six foot three and after all, a small space was always easier to navigate once his prosthesis had been removed. Strike’s only gripe was that the compartment was overheated: he kept his attic flat at a temperature every woman he knew would have deplored as icy, not that any woman had ever slept in his attic flat. Elin had never even seen the place; Lucy, his sister, had never been invited over lest it shatter her delusion that he was making plenty of money these days. In fact, now he came to think about it, Robin was the only woman who had ever been in there.

The train jolted into motion. Benches and pillars flickered past the window. Strike sank down on the bunk, unwrapped the first of his bacon baguettes and took a large mouthful, remembering as he did so Robin sitting at his kitchen table, white-faced and shaken. He was glad to think of her at home in Masham, safely out of the way of possible harm: at least he could stow one nagging worry.

The situation in which he now found himself was deeply familiar. He might have been back in the army, traveling the length of the UK as cheaply as possible, to report to the SIB station in Edinburgh. He had never been stationed there. The offices, he knew, were in the castle that stood on top of a jagged rock outcrop in the middle of the city.

Later, after swaying along the rattling corridor to pee, he undressed to his boxer shorts and lay on top of the thin blankets to sleep, or rather to doze. The side-to-side rocking motion was soothing, but the heat and the changing pace of the train kept jarring him out of sleep. Ever since the Viking in which he was being driven had blown up around him in Afghanistan, taking half his leg and two colleagues with it, Strike had found it difficult to be driven by other people. Now he discovered that this mild phobia extended to trains. The whistle of an engine speeding past his carriage in the opposite direction woke him like an alarm three times; the slight sway as the train cornered made him imagine the terror of the great metal monster overbalancing, rolling, crashing and smashing apart…