‘What is the significance—?’

‘Och, sir, it’s obvious. Schools didn’t like to have pregnant schoolgirls swanning about. Advertises moral degradation, all that shite.’

‘When I was a schoolteacher we had several pregnant girls,’ Perry said.

‘Aye, but that is since the 1996 Education Act, which made it compulsory for teenage mums to complete their education. Back in the 1980s, well, it was still a stain on a school as well as a family. The parents may well have kept her away.’

Frank and Eileen Morris. Perry wondered just what they might have known of their daughter’s activities. If she looked pregnant, they might well have withdrawn her from school. And what did Uncle Harold the fishmonger really see the day she disappeared? As before, the answers could only come from evidence in the present day.

‘Have any DNA samples come to light for our suspect?’ Perry asked.

‘Nope. Every sample we have has been accounted for by a witness or one of us.’

‘That’s a shame, I just had a little theory that I was going to test. But as I’ve got nothing to test it against, I’ll have to leave it.’

‘What’s your theory?’

It seemed so outlandish that Perry was reluctant to tell her. ‘I was just wondering if Jane Morris’ baby grew up to be our killer.’

‘You mean the wee twisted lad hung on to his frozen teenage mum as a kind of keepsake?’

‘Yes.’

‘But that means someone else killed and froze the poor wee hen.’

Perry laughed nervously. ‘It would be just too bizarre, wouldn’t it?’

She put her hands on her ample hips. ‘So you’re looking for someone a bit more normal to be responsible for two stranglings and an abduction?’ Macintosh gave a dry laugh. ‘You could be on to something, sir. It’s just a shame the bomb squad blew up the package containing Sam Gillard’s phone. You could expect a DNA or fingerprint lift off that screen when he was sending messages.’

‘We didn’t get one off Beatrice’s phone.’

‘Aye, that’s because it was smeared in Coca-Cola. That stuff’s super-acidic. One other thing, sir. I checked up the witness you asked me about, Betty Garrison. The dead girl’s grandmother is still alive, at the grand age of a hundred and one, living in a care home in Carshalton.’

Perry set off for Carshalton with a sheaf of cuttings. It seemed like the perfect time to visit, and it had the great benefit of deferring having to go home. He found Mrs Garrison in her private room, sitting up in bed watching TV. She gave him a waspish look, and demanded: ‘Who the hell are you?’ She muted the TV with her remote.

She was a substantial old lady with wattles of blotchy skin hanging down from her chin, and swollen arthritic hands the size and texture of old gardening gloves. Only a few wisps of hair clung to her skull. The care worker who had escorted Perry in had reassured him that Mrs Garrison was still lucid and in control, but did have a bit of a temper. ‘It’s probably what has kept her alive all these years, even after her children have died,’ the woman said.