Perez saw, partly hidden by a bunch of imported roses, the corner of a card and recognized the image just from that. He felt in his pocket for gloves and lifted it out. The black-and-white reproduction of a painting of three fiddle players. The band Fiddlers’ Bid. On the back, no message. He carried it carefully to the car, slipped it into an evidence bag. He knew he should immediately take it back to Lerwick and show it to Willow, but still he continued on his way.

Past Scatsta Airport and the Harbour Authority site: Joe Sinclair’s empire and John Henderson’s second home. Past the oil terminal, with its high security and, next to it, the major construction work to bring the gas ashore. Already the afternoon was drawing into early evening, the colour beginning to drain from the landscape. Cassie would be sitting with her friend at the kitchen table ready for her tea. Really he knew he should turn back, head south. But still he continued until he was driving down a small single-track road towards Hvidahus, realizing only then that this was where he’d been heading all along.

The tiny community was silent. He looked down at the small pier, boats moored ready for the summer. Mark Walsh’s big house waiting for its first guests. The tiny holiday cottage was still empty. The only sound came from the gentle buzz of the wind turbine outside John Henderson’s house. Now that he was here, Perez felt foolish. The house had been made secure and he didn’t have a key. But still he stood there. This place had been built by Henderson and he’d lived here with his wife, nursing her. And this was where he had planned to bring his bonny young wife.

When he was a young DC in Aberdeen, Perez’s boss had been unusual. A strange and thoughtful man, much mocked by his more macho colleagues. ‘Sometimes detection is like acting,’ he’d said once. ‘You have to get inside the offender’s skin, stand in his boots and see the world through his eyes. Understand what makes him tick.’

And this was what Perez did now. He imagined himself as Henderson, a cautious man, who valued routine and order. A man who was struck suddenly, in a thunderbolt from the blue, by a passion for a young woman called Evie Watt. A man who would have handed his love the world and denied her nothing. That thought helped Perez to shake and rearrange the facts as he knew them. Later he would remember nothing of his journey back to Ravenswick because his attention was focused on the characters in the drama. As he drove up to his neighbour’s house he saw Cassie looking out of the window towards the Ravenswick Hotel. He stopped the car and followed her gaze, and for a moment he saw how the murders might have happened – Willow’s mirror made whole.