‘Bear with me,’ he says, glancing at his notes again on the screen before switching to an academic paper he’s just found on the Internet. ‘From what I can gather, a super recogniser like Kate has a more developed fusiform gyrus.’

‘What’s that when it’s at home?’

‘The area of the brain that processes faces – the same area that was affected by her accident.’

‘And how does that relate to Capgras?’ Bex asks. Jake’s in danger of losing her.

‘Because Capgras can also be caused by traumatic brain injury – specifically, lesions in the fusiform gyrus.’

‘Bloody hell, that must be what she’s got then. It would explain everything.’

Jake can hear the relief in Bex’s voice. ‘Except that it’s an extremely rare and unusual disorder,’ he says, reading from the article again.

‘Someone’s got to have it.’

He’s still not convinced. ‘And it doesn’t seem to affect the auditory cortex, just the visual.’

‘Say that bit again,’ Bex says, a sudden curiosity in her voice.

‘Someone with Capgras only thinks their loved one is a double if they can see their face,’ he explains. ‘If they can only hear their voice, it doesn’t seem to affect them.’

‘When they’re talking on the phone, you mean?’

‘I guess so. Why?’

‘Because Kate says she’s fine when she’s chatting to Rob on her mobile. It’s when he facetimes her and she can actually see his face that she freaks out.’

Jake sits up in his chair, trying to get his head around what Bex has just said. ‘You really need to speak to her about this,’ he says. Up until now, the Capgras theory has seemed interesting but a little fanciful. He now thinks they might be onto something, given her past as a super recogniser. It would be a cruel irony if a high-performing fusiform gyrus, once responsible for Kate’s exceptional powers of recognition, was now tricking her into seeing doubles.

‘She’s seeing a neuropsychiatrist regularly,’ Bex says. ‘Paid for by Rob. I’ll get her to ask him about it. I don’t think she’s mentioned seeing doubles to him yet.’