‘Nursing home killings often come from a build-up of frustration or work stress. Occasionally, there’s an underlying condition like Munchausen’s by proxy or angel-of-death syndrome that attracts carers into the profession in the first place.’

‘If that were the case, I’d expect there to have been other unexplained deaths there.’

‘Because we don’t have enough to deal with at the moment?’ Ava raised her eyebrows. ‘It could have been a new staff member, a temp. Other deaths could have been expected but just hastened, meaning there’d have been no postmortem. A lack of evidence doesn’t mean this is an isolated incident. It’s the hardest possible environment to make sure all deaths are natural. I’m only telling you so you can relax about it a bit. Graham’s a good detective. He’ll figure it out.’

Callanach nodded. ‘Okay,’ he conceded. ‘I’ll start sifting through the Hawksmith information. Good luck with Overbeck.’

Back at his desk, he checked his emails. There were a few from Lance – responses to his article that should have gone straight to MIT but that had gone to him. There were a few adverts that had escaped the trash folder and some online bills. Below that was a bounce back from the email he’d sent his mother. He felt suddenly sick. The last time an email to his mother had bounced back was when she’d disappeared from his life while he was fighting the rape allegation. That time it had been deliberate. She’d needed to get away from the whole dreadful situation and the memories it was dragging up. But in Paris she’d seemed fine. They’d undone most of the damage and reclaimed the close relationship they’d enjoyed before. Now this …

Callanach read his original email, checking the address he’d entered carefully for typos. There were none. Hitting resend, he doubled it up with a text to her, explaining that he’d tried to contact her but failed, hoping there was nothing more serious going on. It was difficult enough to bring up the subject of Bruce Jenson’s death without worrying that his mother wasn’t coping again.

Sergeant Lively’s face resembled a punctured beach ball. Ava pointed at the empty chair opposite her desk as she finished typing a note requesting extended funding for forensic testing at Tantallon. It was a low trick to get Lively to request it for her, but it wasn’t as if Detective Superintendent Overbeck could complain publicly about it.

‘I need you to use your considerable influence with the super to get a full crime scene workout at Tantallon Castle,’ Ava smiled at him. ‘I’m just finishing my notes, then I’ll hand this straightforward administrative task over to you.’

‘The Tantallon file’s closed,’ Lively said. ‘Dr Lambert decided it was suicide gone badly wrong, but nonetheless suicide.’

‘Yeah, only that would make two in a row,’ Ava replied quietly.