Ideally, DI Wilson, but glancing in at the door, Magnus saw that Bill was deep in conversation with McCreadie and Rhona at that moment. However, both McNab and DS Clark were heading his way, so Magnus made up his mind to approach them in the first instance.

Catching DS Clark’s eye – McNab wasn’t acknowledging his presence – Magnus called her name.

With a quick aside to McNab, who seemed intent on going somewhere, and swiftly, DS Clark approached Magnus.

‘Professor Pirie, you heard what was said about Alec McLaughlin at the meeting?’

‘I did. May I have a word with you?’

She looked unsure. ‘Is it about the McLaughlin interview, because it’s probably better if DS McNab’s there too, and he’s had to go out.’

Magnus briefly wondered whether that was true or McNab was in fact just set on avoiding him.

‘It would be better if we three sat down together about that, although I thought it went very well,’ Magnus said. ‘I’ll send you both my thoughts via email. However, what I wanted to say is some new information related to the Mary McIntyre case.’

Janice looked interested. ‘Shall we get a coffee in the canteen then?’

Magnus was happy to agree, preferring the cafeteria to an interview room.

Collecting their coffees, Janice led Magnus to a quiet corner.

‘So,’ she said, once they were seated. ‘Fire away.’

Not for the first time did Magnus think how much easier it was to talk to DS Clark than McNab. And not for the first time did he try and analyse why that was. Dysfunctional relationships went both ways. Magnus found McNab’s sharp edges and cynicism difficult to handle at times. As for McNab, Magnus wasn’t sure whether the detective didn’t like him personally or whether he didn’t like what Magnus represented – the world of forensic psychology.

And yet, he thought briefly, when they did work together, like in the sin-eater case, their combined knowledge of the criminal mind often resulted in success.

‘What did you want to run past me, Professor?’ DS Clark’s enquiry broke into his thoughts.

‘I’ve been visiting a number of recovery cafes over the past couple of months,’ Magnus told her. ‘I assume you know about these?’

DS Clark nodded.

‘Well, while visiting Barlinnie recently, actually to interview Mr McLaughlin, I bumped into Pat Robertson, who was there with three colleagues to run the in-house cafe.’ Magnus checked to see if DS Clark was following him.

‘Go on,’ she said.

‘Anyway, I hadn’t seen her since she’d taken me for a session at the women’s recovery cafe in Raploch in Stirling.’

At the mention of Stirling, DS Clark’s interest seemed to grow.

‘Anyway, I exited the strategy meeting to take a call from Pat.’ Magnus paused. ‘It turns out that Karen Johnston, who is part of their group, is in fact Karen Marshall, Mary McIntyre’s best friend at the time of her disappearance. She married a man called Jack Johnston and lives in Stirling.’