‘She thought they must be ancient. Another theory down the drain. But she’s fast-tracked them for testing and she’ll let me know as soon as she can.’

The airport was quiet and they sat drinking coffee at one of the tables outside the shop.

‘Have you read all the letters?’ Perez was watching an elderly couple in conversation with the guy at the check-in desk. Sandy followed his gaze. They were holding hands. Gross, he thought. At their age they should keep that sort of thing for their own home.

‘No. Only the most recent one.’ Of course, Sandy thought, I should have looked at the letters. Perez would have stayed up all night reading them, worrying at them. He wouldn’t have got pissed on expensive lager in the hotel bar and fallen into a drunken sleep. In the plane on the way home Sandy had read a glossy men’s magazine with a topless model on the cover; he hadn’t really given a thought to the case.

But Perez made no comment. ‘What was your impression of Gwen James?’

‘Like you said, she felt guilty. She’d done what she thought was the best for her daughter.’ Sandy found himself wanting to show Gwen in a good light. ‘She didn’t want to intrude on Hattie’s life but you could tell she cared about her. I mean, work obviously takes up a lot of her time but that didn’t stop her worrying.’

‘Does she think Hattie killed herself?’

‘She says that Hattie talked about wishing she was dead when she was very depressed but she’d never attempted suicide. And she doesn’t think Hattie was so depressed at the moment. All winter in the university she’d been positive, looking forward to getting back to work in Whalsay. The last letter seemed to be about plans for the future. It was only the phone call that really worried her.’

‘And we can listen to that?’

‘Yes, I’ve brought back the SIM card.’ Sandy had checked his pocket at least a dozen times to make sure it was still there. Now he took it out and gave it to Perez, pleased to be relieved of the responsibility. ‘I said she could have it back once we’ve finished with it. It’s the only record she has of Hattie’s voice.’

‘Of course. You did well to persuade her to let you have it.’

They’d finished their coffee. Sandy had the impression that there was something else Perez wanted to say. They sat for a moment in silence.

‘Should we go then?’ he said at last. He’d never had Perez’s patience.