“Sorry,” he muttered when he had sat back down and taken a long pull on the pint. “Thinking about stuff I haven’t thought about for a long time. Those bloody lyrics.”

“Yes,” said Robin.

“For fuck’s sake, it can’t be Digger,” said Strike in frustration, running a hand through his dense, curly hair and leaving it entirely unchanged. “He’s a professional gangster! If he’d found out I gave evidence against him and wanted retribution he’d have bloody shot me. He wouldn’t fanny about with severed legs and song lyrics, knowing it’d bring the police down on him. He’s a businessman.”

“Does Wardle still think it’s him?”

“Yeah,” said Strike, “but he should know as well as anyone the procedures on anonymous evidence are watertight. You’d have coppers lying dead all over town if they weren’t.”

He refrained from further criticism of Wardle, though it cost him an effort. The man was being considerate and helpful when he could be causing Strike difficulties. Strike had not forgotten that the last time he had tangled with the Met they had kept him in an interrogation room for five solid hours on what appeared to be the whim of resentful officers.

“What about the two men you knew in the army?” asked Robin, dropping her voice because a group of female office workers were settling themselves at a table nearby. “Brockbank and Laing. Had either of them killed anyone? I mean,” she added, “I know they were soldiers, but outside combat?”

“It wouldn’t surprise me to hear Laing had done someone in,” said Strike, “but he hadn’t, as far as I know, before he went down. He used a knife on his ex-wife, I know that—tied her up and cut her. He spent a decade inside and I doubt they managed to rehabilitate him. He’s been out over four years: plenty of time to commit murder.

“I haven’t told you—I met his ex-mother-in-law in Melrose. She reckons he went to Gateshead when he got out of the nick and we know he might have been in Corby in 2008… but,” said Strike, “she also told me he was ill.”

“What kind of ill?”

“Some form of arthritis. She didn’t know the details. Could an unfit man have done what we saw in those photos?” Strike picked up the menu. “Right. I’m bloody starving and you haven’t eaten anything except crisps for two days.”

When Strike had ordered pollock and chips and Robin a plowman’s, he made another conversational swerve.

“Did the victim look twenty-four to you?”

“I—I couldn’t tell,” said Robin, trying and failing to block the image of the head with its smooth chubby cheeks, its frosted-white eyes. “No,” she said, after a brief pause. “I thought it—she—looked younger.”

“Me too.”

“I might… bathroom,” said Robin, standing up.

“You OK?”

“I just need a pee—too much tea.”

He watched her go, then finished his pint, following a train of thought he had not yet confided to Robin, or indeed anyone else.

The child’s essay had been shown to him by a female investigator in Germany. Strike could still remember the last line, written in neat girlish handwriting on a sheet of pale pink paper.