Rhona watched as J. D. considered this. ‘You’ve not found the evidence boxes?’

‘Not as yet, but we’re still looking,’ Bill said.

‘I don’t think Dr MacLeod needs me to tell her how primitive it was in terms of forensics. She deals with it in her lecture on the World’s End case, specifically with that startling image of the row of plods standing six inches from the body on the beach. Now that made me grue when I saw it, although it was standard practice at the time.’

He continued, ‘Bear in mind it was a missing child and not a crime scene or a deposition site we were dealing with.’ He looked to Rhona. ‘So all we could really do was map out her movements and interview any suspects.’

‘What, if any, material was taken from the suspects?’ Rhona said.

‘If it had been a murder enquiry, then fingerprints, blood type, maybe fibres. But this wasn’t a murder. So fingerprints only, which apparently we no longer have.’

Everything he’d said just confirmed what Rhona already suspected. The dress found with the body was the only real link they had with the killer.

‘What you said in the strategy meeting about the dress and the DNA you’ve located so far not being from Mary . . .’ J. D. said.

Rhona waited.

‘It reminded me of something I’d forgotten.’

‘Go on,’ Bill said.

‘It was odd, but her mum said the school clothes Mary was wearing before she got dressed up for the confirmation were missing from her bedroom.’

‘And you never found them?’ Rhona said.

‘No. We assumed she’d taken them with her to change into later.’

‘But she was coming back to the school, which was across the road from her house,’ Rhona said. ‘Why would she take a change of clothing with her?’

J. D. nodded. ‘We wondered if she’d planned to go to the den she had with Karen and maybe change there, so as not to mess up her dress.’

‘Did you ask Karen about this?’

‘When she did talk, she just kept saying how much Mary loved her dress. Then she shut up altogether.’

Karen was key to all of this, if they could locate her, Rhona thought. Even down to the actual dress Mary had worn that day.

‘I’m not convinced Mary was wearing the dress we found in the grave, either when she was killed or even when she was moved to the deposition site,’ Rhona said. ‘So maybe she was dressed in her normal clothes. Did her mother describe them?’

‘Her usual school clothes: a hand-knitted blue woollen jumper and grey pleated skirt, white ankle socks and leather sandals.’

Rhona thought back to the trace samples they’d retrieved from the clothes and, in particular, the body. The taping she’d done in the grave before they’d taken the body to the mortuary had resulted in mostly peaty deposits, as she’d suspected, but not only that. There had also been microscopic pieces of hair, like shavings.