Cooper sighed. ‘You’ve obviously made your mind up about Freddy Robertson on no evidence. Is this some kind of intuition, Diane?’

‘Intuition, bollocks. This is experience. I’ve met enough weirdos to know one when I see one.’

‘Fair enough.’

‘So is the professor married?’

‘I don’t know. He’s never mentioned a Mrs Robertson.’

‘Can you find out?’

‘I suppose so.’

Cooper’s assumption had been that Robertson was a bachelor, or divorced. Men with obsessions were difficult to live with. But you could never be sure – it was remarkable the compromises people could come to in their relationships.

‘Oh, I forgot to tell you,’ said Cooper. ‘I had a really bad time at Mrs Gill’s. All the family were there, getting ready for the funeral this afternoon. Audrey Steele’s second funeral, that is. They interrogated me about how we were doing with the enquiry.’

‘What did you tell them?’

‘There wasn’t much I could tell them. They weren’t very happy with that. I was glad to get away before they formed a lynch mob.’

‘These jobs have to be done.’

The outcrop called Peter’s Stone or Gibbet Rock stood towards the north end of the Cressbrook Dale nature reserve, an area of limestone grassland, with ash woodlands further down the dale. There was a path along the stream into the dale, reached through a tiny, spring-loaded gate and a gap in the stone wall that was just wide enough for a slim person not wearing too many clothes. Cooper thought he would probably manage to squeeze through, as long as he was trying it before lunch and not after.

‘There must be another way,’ said Fry, looking at the fields full of sheep. In the bottom of the dale, the rushing stream looked impossible to cross.

‘Yes, I think there is.’

Right at the junction of the Wardlow road, they found a gateway in a farmyard, just wide enough for Cooper’s Toyota to scrape through, past a mildewed hawthorn tree. The gate was secured only by a length of orange baler twine looped over the stone gate post. The four-wheel drive managed fine on the track until they came to a point where the swollen stream had breached the field wall and swamped the ground on the other side. Cooper stopped and looked up at Peter’s Stone, still two hundred yards away.

‘We’re going to have to walk, I’m afraid.’

Fry opened the passenger door and looked down at the water lapping gently against the wheels. ‘I’m not getting out on this side.’

‘It’s deep, but clean.’

‘I’m not getting out.’

‘I can lend you some wellies,’ said Cooper. ‘They’re in the boot.’

‘OK.’