DS Clark’s eyes lit up. ‘That’s excellent news. Is she going to make contact with us?’

‘That’s not a certainty,’ Magnus said. ‘According to Pat and the group’s leader, Marge, Karen’s been in a very delicate and often confused state since the death of her husband from dementia, and she left the meeting abruptly before the TV appeal with Mary’s siblings. They don’t know if she saw it, but up to now she has refused to put herself forward, suggesting it wasn’t necessary, since they hadn’t identified the body as Mary’s.’

‘But we have now, and she’s a key witness,’ DS Clark said. ‘Do you have this woman’s contact details?’

‘I have her mobile number, which she isn’t answering, according to Pat. The group don’t have her address.’

DS Clark considered this. ‘We can trace her through her mobile.’

‘It’s a pay-as-you-go,’ Magnus said.

‘Okay. There are other ways. You said her husband died recently?’

‘Within the last year, I believe.’

‘So we contact social services, check funeral parlours, find her doctor’s practice.’

It all sounded straightforward, yet Magnus could foresee the difficulties even after they’d located Karen.

‘This woman is already traumatized,’ he said, ‘and from what Pat says, the discovery of Mary’s body could have made things worse.’

Janice waited as he explained further.

‘Apparently she was having flashbacks about Mary’s disappearance even before the body was discovered. Finding out it was her friend might have brought back terrible memories.’

‘Memories we are keen to ask her about.’ DS Clark rose. ‘I need to get started on this, Professor. Thank you for bringing it to us.’

‘If or when you find her, I would urge caution on how you question her. Childhood traumas are deep-rooted, often buried well down in the psyche and devastating when they finally surface.’

DS Clark gave him a studied look. ‘I have every intention of asking the boss to bring you in on this. The help you gave us regarding the McLaughlin interview was invaluable.’ She raised an eyebrow. ‘Even though my partner may not have given that impression.’

Watching her leave, Magnus was conscious that, having been entrusted with the information about Karen Johnston, he had now just handed it over to the police.

Was that what Pat, or even Marge, had intended?

He’d asked Pat what he might do to help. Her advice had been to find Karen whatever way he could. Pat knew he would go to the police, because that was the quickest and most efficient way to contact Karen, but still Magnus wasn’t sure it was the best way.

He pictured Karen again, sitting opposite him at the meeting. Magnus could see, looking back now, the struggle it had taken her to get herself there. If she was so fragile back then, what might her state of mind be now?

He pulled out his phone. As requested, Pat had texted him Marge Smith’s number, with the message,

She knows more about Karen’s state of mind than me. I only visit the cafe on occasion.