‘Deborah Rawson says she believed her husband was having an affair,’ said Fry, ‘and that might be true. But I think Patrick Rawson did something quite unforgivable in Deborah’s eyes, and it wasn’t to do with another woman.’

‘What?’

‘He proved that Erin Lacey was right about him. At heart, he was just a dodgy Irish horse dealer. That must have been the killer for Deborah Rawson.’

‘What – the fact that he’d gone back to horse dealing when she thought he was becoming a respectable businessman? Or the fact that Erin Lacey had been proved right?’

Fry nodded. ‘Both. There was certainly no love lost between those two women. So it was a double whammy. Can’t you just hear Mrs Lacey’s reaction?’

‘“Blood will out” – that sort of thing.’

‘Exactly.’

‘So if he hadn’t been tempted by the call that Naomi Widdowson made . . .’

‘He might still be alive now. Yes, that was what sealed his fate, I’m sure of it.’

‘But Deborah would rather let people think that he was having an affair, betraying her with another woman.’

‘Image,’ said Fry breathlessly. ‘It’s all about image.’

From Black Harry Gate, a path ran eastwards through a steep-sided dale that squirmed its way towards Calver. But Cooper continued to lead the way towards the rakes on Longstone Moor, where the sheep were still playing chicken with the quarry lorries. Who would be the last to get out of the way? From the stubborn expressions on their faces, these sheep didn’t realize how unequal the confrontation was.

Finally, he stopped to allow Fry to get her breath, and looked out over the patchwork of fields. The sun was breaking sporadically through the clouds, highlighting one field and then another, changing the colours in the landscape as it went, catching a white-painted farmhouse, casting faint shadows from a copse of trees.

The tracery of white limestone walls was spread out before him like a map laid over the landscape. Cooper sometimes thought that if you just followed the right lines in that map, you could discover any story you were looking for, find the right clues to any mystery. All the answers seemed to lie in this gleaming web, so painstakingly constructed that they almost held the countryside together.

And there was still a question to be answered. The charges against Naomi Widdowson and Adrian Tarrant ought to feel like a conclusion. But instead, it was quite the opposite. The death of Patrick Rawson now felt like a distraction. The real mystery was what had happened to his partner.

Officers in blue boiler suits were still working their way along the edge of Longstone Moor, trying to pick up traces of Michael Clay.

‘Hey, look,’ said Cooper. ‘It’s Sitz, Platz, Holen and Bissen.’

He looked at Fry, to see if she’d heard the joke around the office. Derbyshire Constabulary had recently been buying German-speaking police dogs, which meant that dog handlers had to learn the German commands to make their dogs work properly. Some wag had named the dog handlers after the German commands for sit, stay, fetch and bite: Sitz, Platz, Holen and Bissen.