He started to speak, directing his words at Ronald as if they were the only people in the room, talking only just loudly enough for the tape machine to pick up his voice. ‘It’s the war. We have three brave Whalsay men working with the Shetland Bus: Jerry Wilson, Cedric Irvine, whose son now runs the Pier House, and your grandfather Andy Clouston. Saving lives. Then along comes a young Norwegian man. Per. He was brave too and deserves the dignity of a name. He’d come to Britain for a special purpose, more an accountant than a soldier, to collect money to finance the work of the resistance.’

Ronald’s eyes widened.

‘How do I know that?’ Perez went on. ‘Because a detective digs into the past. I’m an archaeologist too. I’ve spoken to the Norwegian Embassy and to historians here in Shetland. When Per disappeared he was carrying a fortune in Norwegian currency, sealed up in half a dozen tobacco tins.’ He looked up. ‘It sounds like a child’s tale, doesn’t it? An adventure story or one of the trowie myths. Buried treasure. Unreal. But it was real enough at the time. Until the fortune disappeared and everyone assumed that Per had turned traitor and taken the money with him.

‘But Per was a brave and honest man. Mima was a wild woman even then, and she’d been flirting with the good-looking stranger, who was kind to her, kinder than her husband would ever be. Jerry Wilson found them in bed together, lost his temper and killed the man. And disposed of the body with the help of his friend, who just happened to be a Clouston. Old Andy Clouston, your grandfather. News of the man’s disappearance got out, as it always will in a place like Whalsay, so they put around stories of their own: one of the tales, passed down to Cedric, was that Per had been a traitor.’ Perez paused. He wished he’d thought to bring a bottle of water into the interview room. His throat was dry and he felt light-headed through lack of sleep. He looked up at Ronald, who must have been exhausted too. He could have had no real rest since he started killing.