There was a moment of silence. ‘Why would I?’ Henderson said. ‘We bring the tankers in and then we take them out. Then we leave. We have no real contact with the terminal.’ He looked at his watch again – the only indication that the interview was starting to irritate him.

‘Where were you on Friday night?’

‘I was here,’ Henderson said. ‘Catching some sleep because I was on call.’ He stood up. ‘Now is there anything else, Sandy? I should be getting back to work.’

‘Were you called out to work on Friday night?’ Sandy asked.

‘Not until the early hours of Saturday morning.’ Henderson seemed almost amused by the question, but again Sandy had no real idea what he was thinking. ‘But I have no proof for you. No witnesses. They don’t lock us in.’

Outside a helicopter came in to land at Scatsta. The noise was very loud and the room seemed to shake. Sandy thanked Henderson for his help and left the building. As he walked to his car a group of men in identical blue overalls stared at him. He felt as if he was in one of those cowboy films he’d watched as a kid – the stranger riding into town.

In Lerwick the morning briefing was just breaking up. There was a whiteboard on the wall and Willow Reeves was staring at it, absorbed, as if the solution to the case was captured there in the scrawled names and photos. She didn’t notice the rest of the team leaving or Sandy coming in. He coughed to get her attention and she turned, startled.

‘We still don’t know where the man was killed,’ she said. ‘There’s no crime scene. If we had that, maybe we could move the investigation on. There’d be some forensic trace. It’s driving me crazy. It’s as if Markham drove out of Sullom Voe in the fog and then disappeared. How did his body get from there to a boat in the marina at Aith, and his car back to the museum? What did he do that triggered those events?’

‘He gave somebody a lift?’ Sandy said. ‘Anybody walking along a road in the country, you’d stop and see if they needed a ride. Specially in that weather.’

‘And would Markham do that too?’ Willow demanded. ‘Snooty Markham, who’s used to city ways.’

‘Maybe it would depend who it was.’ Sandy was thinking, struggling to keep up. Willow seemed to jump from thought to thought, to build links and conclusions while he was still beginning the process. ‘He always had a reputation for liking a pretty girl, even before he got Evie into trouble.’

‘Could he have bumped into Evie on the road?’ Willow asked. ‘I still can’t get my head round the geography of this place. Wherever I look there’s water. It’s disorientating.’