‘Most married couples do have disagreements,’ said Lowther stiffly. ‘As I said, we all went through a bad period during the adoption, which put a bit of pressure on everybody. Tensions spill over now and then. But recently . . . ?’

He looked at his wife, who seemed even more reluctant. ‘If they had problems, then it was a personal matter between themselves. Young women don’t tell their mothers everything these days, I’m afraid.’

‘Mr and Mrs Lowther, where is your son-in-law?’

Neither of them answered her, and she began to get angry.

‘And your granddaughter? She isn’t here today. So where is she? Where are Brian and Luanne?’

The Lowthers looked at each other again.

‘We don’t know.’

Fry’s mobile rang, and she saw from the display that the call was from Gavin Murfin.

‘Excuse me a moment.’

She stepped outside on to the terrace to take the call, while the Lowthers sat and watched her.

‘Diane, you’ll want to know this straightaway,’ said Murfin. ‘I persuaded someone in West Yorkshire to make a few enquiries into John Lowther’s spell there.’

‘Well done, Gavin.’

‘Well, I didn’t have time myself. So that’s another favour I’ll have to repay.’

‘Did they turn anything up?’

‘I got a call a few minutes ago. They say John Lowther was a psychiatric patient in Leeds for three months. That’s why he had to leave his job.’

‘Did you go to Matlock to speak to him?’

‘I’m at his apartment now. But John’s not home. And the neighbours say they haven’t seen him since yesterday.’

‘Oh, great,’ said Fry. ‘The Lowthers are really, really going to love me.’

Moira Lowther was in her garden when Fry returned to the house. Perhaps she went out there to escape from the plants. When she heard what Fry wanted to talk about now, she sat down unsteadily in one of the chairs set out on the decking.

‘John is psychotic, not a psychopath,’ she said. ‘There’s a big difference.’

‘Yes, I’m sure.’

Her husband stepped out of the sliding doors from the conservatory, and stood next to his wife, his jaw stiff with emotion.

‘People don’t understand that they’re entirely different things,’ said Mrs Lowther. ‘Psychosis isn’t characterized by a tendency to violence towards others. They’re a risk to themselves, but no one else. Psychotics aren’t manipulative either, the way psychopaths are. But how many people do you think register that difference? To them, it’s all the same.’

Her husband leaned forward to put in his own comment. ‘But then, we’re talking about the sort of person who can’t distinguish a paedophile from a paediatrician. It’s sheer ignorance. Some people wallow in it.’

Mrs Lowther looked up at Fry. ‘So our son is psychotic,’ she repeated. ‘Not a psychopath.’

‘Yes, I understand.’

‘Do you?’

‘Actually, yes. I do.’