The A623 took traffic through sheep pastures and across the plateau towards Manchester. Almost as soon as Cooper turned on to it, he sensed the landscape opening out on his left. In a gap between the hills stood a strange, isolated outcrop of limestone. Its distinctive shape looked almost artificial – straight, pillared walls of white rock split by crevices and fissures, and a rounded cap grassed over like a green skullcap. The slopes of short, sheep-nibbled grass around it seemed to be gradually encroaching on the limestone, as if reaching up to pull it back into the ground.

The rock looked familiar. Searching his memory, Cooper thought it might be called Peter’s Stone. He had no idea what the name meant, but guessed it was probably some biblical reference to St Peter, the reasons for it lost in the passage of time and the mists of folklore.

‘Can I listen to the tapes some time, Diane?’ he said.

‘Don’t imagine you’ll recognize the voice. It’s electronically disguised.’

‘I might have some ideas, though.’

‘Yes, OK. Remind me when we get back.’

‘Thanks.’

Fry tapped a finger on the map. ‘Ben, we should be going the other way. Eyam.’

Cooper pulled over and reversed into the Litton turning. ‘By the way,’ he said, ‘my unidentified remains were found at Litton Foot, in Ravensdale.’

‘Yes? What about them?’

‘Litton Foot is less than three miles from Wardlow across country. It falls within your circle.’

Fry looked at the map. ‘But your body is eighteen months old, Ben.’

‘I know.’ Cooper shrugged. ‘I just thought I’d mention it.’

‘Tell me about Eyam.’

‘For a start, it’s pronounced “Eem”. The village was infected by the plague from some infected cloth, but the villagers quarantined themselves so they wouldn’t spread it to the rest of Derbyshire.’

‘When was this?’

‘Seventeenth century.’

‘OK.’

‘Well, three hundred and fifty people died in Eyam. The names of the victims are recorded on some of the cottages. Plague victims couldn’t be buried in the churchyard, so their graves are in the fields around the village. Whole families together sometimes.’

‘Are these places well known?’

‘Well known? They’re a tourist attraction.’

Back at West Street, Diane Fry disappeared for a meeting with the DI before the evening briefing, and Cooper didn’t get a chance to remind her of her promise. So instead of listening to the tapes, he took the opportunity to spread out the photos of the human remains found in Ravensdale.

The quality of crime scene photography had improved tremendously since the photographic department spent money on replacing its printing equipment. Colours had started to bear some relationship to reality, instead of looking like snaps taken by a passing tourist with a Polaroid. Now you could see that the stuff on the floor near a body was actually blood, not the corner of a donkey-brown rug.

Outdoors, they sometimes managed to get quite interesting lighting effects. In one of the Ravensdale photographs, Cooper could make out the dappling effect of sunlight through the canopy of trees. The sun had swung round to the south by the time the shots were taken, so it must have been around the middle of the day. The photographer would have been wondering when he’d get a chance for his lunch.