‘Well, Billy McGowan must have felt some sympathy for him. If someone like McGowan was willing to keep quiet about Vernon’s arrangement with Professor Robertson, then Vernon must have had something about him that I couldn’t see.’

‘I suppose so.’

Fry looked at the door of the interview room. ‘That still doesn’t explain why the old man killed him. Why did he do that?’

On the other side of the door, Abraham Slack sat looking at the triple-deck tape machine with a dead stare, devoid of emotion. Even the tapes had ceased to record his silence.

Ben Cooper was in the kitchen of Greenshaw Lodge when Fry found him later that day. He’d been watching the house gradually become sparser and more empty as the forensic team carried away items for examination. In the sitting-room display cabinet, he could still see the photograph of Abraham Slack and his family, though the SOCOs’ lights reflecting off the glass made the individual figures impossible to identify.

‘There was something about the way Vernon spoke,’ he said, when Fry negotiated the safe path to reach him. Cooper was trying to get his thoughts clear in his own mind, and Fry was the only person he thought might understand.

‘Shouldn’t you still be in hospital?’ she said.

‘They’ve stitched me up and given me a tetanus jab. There was no point in staying there any longer.’

She looked at his bandaged foot. ‘No bones broken or anything? I’ve seen such horrible stories about animal traps.’

Cooper shook his head. ‘The trick is to lie still and minimize injury. Animals don’t know that, so they end up tearing their own legs off.’

Fry grimaced. ‘What do you mean about the way Vernon spoke?’

‘When I talked to him, he never once said “I” or “me”. It was always “we” or some passive form, like “There’s a job to be done”. Most people would have said “I’ve got a job to do”. But when Vernon spoke, he made it sound as if none of it was anything to do with him personally. It was as though he was distancing himself from the whole thing.’

Cooper looked at Fry to see if she was listening. She was studying the marks of the shotgun pellets in the wall, where Abraham Slack had loosed off his first, and wildest, shot. The cartridge case had been found in the hallway, near the foot of the stairs.

‘It’s exactly what Dr Kane said about some of the phrases used in the phone calls,’ he said. ‘An unconscious form of denial, suggesting underlying guilt.’

‘So Vernon made the phone calls?’ said Fry.

She was trying to sound as though it was a minor detail. But Cooper knew that the calls were very important to her.