‘There’s a syndrome … I can’t remember what it’s called. He’s not acting the way a rational person would. This isn’t just accelerated behaviour, it’s beyond all normal parameters. So maybe he’s acting as if he’s invisible because he genuinely believes he is. He feels no fear, has no sense of consequences. There’s little attempt to cover his identity. When he was asking me about my achromatopsia, he said …’ She flicked hurriedly through her notebook. ‘Here it is, “The world you inhabit is not the same as everyone else’s. Mine is even less so.”’

‘Sounds like science fiction.’ Baarda joined her in front of her laptop.

Connie typed the terms ‘mental disorder, belief in death’ into the search engine and waited for results to come back. The top few results were either true crime reports, studies in faith in life after death, or zombie movie references, followed by a reference-book-style definition.

‘Cotard’s delusion,’ she read aloud. ‘See also Cotard’s syndrome or walking corpse syndrome. It’s extremely rare, but there are documented cases. The affected subject mistakenly believes that they do not exist, that they’re dead or in the process of dying, sometimes that their organs are in the process of putrefying, or that their body is decaying. Sometimes sufferers believe they are immortal. Named for the nineteenth-century neurologist Jules Cotard, who first diagnosed it as a syndrome. I read about it when I was studying, but cases are too rare to expect to find one in the course of normal practice.’

‘Apart from the risk-taking, why is it you think this syndrome fits our case?’

‘He’s so thin we have witnesses describing him as almost skeletal. It’s a regular feature in Cotard’s. Sufferers believe they no longer need to eat. Look,’ she pointed to a footnote on the screen, ‘there are documented cases where the sufferers ended up dying of starvation. The evolution of his offending hasn’t matched any other known profile. That’s because he was reacting to his perception of his illness. Believing that he was dying but not yet dead allowed him the time to be careful and studious with Angela Fernycroft. When that went wrong, there was a downward spiral. His own perception of his demise would have increased. He became desperate, taking hostages faster. And he used a really weird phrase that I misunderstood.’ She flicked through her notes again. ‘Here we go. He said, “I have to pass this time.”’

‘So he believes he’s running out of time on this earth?’ Baarda asked.

‘Maybe. Imagine what you might be capable of if you genuinely believed you were dead.’

‘Consequences would become irrelevant. The police, the courts, prison. None of it would matter. He’s capable of absolutely anything.’ Baarda stuck his hands in his pockets and wandered to the window. ‘So what’s the relevance of Elspeth, Meggy and Xavier?’