Cooper had been given the impression that the professor had retired to Derbyshire, but this wasn’t strictly true. Totley was an outer suburb of Sheffield, and it lay in South Yorkshire. But the county boundary was only a stone’s throw away across the fields, and the national park a few hundred yards further on. The rural setting was one of the attractions for those who could afford to live here.

Cooper had spent the drive to Totley listening to a Runrig CD. ‘The Edge of the World’ didn’t quite describe his journey across Froggatt Edge and the eastern moors, but it came close.

‘This is an Edwardian gentleman’s residence,’ said Robertson, meeting Cooper at his car. ‘As you can see, we had it refurbished in a manner sympathetic to the Arts and Crafts movement. Four bedrooms on a galleried landing, original beams, a wine cellar. And look at these gardens –’

The professor was a big man in his early sixties, his hair greying and rather too long at the sides to compensate for the bald patch at the front. He wore a rather baggy pinstripe suit like a lawyer’s, and moved a little stiffly, as if suffering from the first symptoms of arthritis.

They entered an L-shaped reception hall with mosaic tiles on the floor and a staircase with mahogany balustrades. On the wall was the ugliest coat rack Cooper had ever seen. It was covered in imitation deer hide, and had four real hooves turned upside down to act as hooks.

Robertson took him through into a study lined with books, the floor space almost filled by an oak desk and a set of deep leather armchairs. The professor sat at his desk, with his back to a window looking out on to the garden. He offered Cooper a drink, which he refused, but poured himself a whisky from a bottle of Glenfiddich he took from a cupboard. Then he linked his fingers, like a headmaster with an errant pupil on the carpet.

‘I’m sorry to have messed you around, sir,’ said Cooper. ‘I hope I haven’t disrupted your afternoon too much.’

‘Oh, I’m glad you could make it. I was worried that you’d decided you didn’t need to call on my services after all. But I suppose you were detained on urgent police business?’

‘You might say I had to speak to a man about a dog.’

‘Oh, dogs,’ said Robertson. He sniffed suspiciously, as if Cooper might have smuggled one into the house, or at least brought in the smell and a few stray hairs. ‘Now I’m really wounded, Detective Constable. I’d have been happy to come in second to anybody or anything, except a dog.’

Cooper smiled hesitantly, not sure whether the professor was joking.

‘You don’t like dogs, sir?’

‘I find their form of domestication offensive, on an ethical basis.’

‘I’m sorry?’