She drops a crumpled can of Coke into her bucket, which also sports Rob’s company name, and looks up, staring back towards the village and the surrounding countryside. Is his double really down here somewhere? Watching them? And what has he done with her Rob? The Rob who has taken care of her for the past five months, nurtured and loved her with such tenderness.

‘There is another explanation for all this,’ Bex says.

‘I told you, he doesn’t have a twin.’

‘It’s not that.’ Bex pauses, looking around the beach. ‘Have you heard of something called Capgras syndrome?’

‘No, why?’ she asks. It sounds French, like a resort on the Riviera. ‘Should I have done?’

‘Jake was telling me about it yesterday. It’s a…’ Bex hesitates. Unusually for her, she seems to be choosing her words carefully. ‘It’s a state of mind, a condition, where someone thinks that the person they love has been replaced by an impostor, a double.’

‘A state of mind?’ Kate says. Bex is not being straight with her. It sounds more serious than that. She’s also been chatting with Jake about her, which is unsettling.

‘OK, it’s an illness,’ Bex says. ‘A delusion.’

‘I’m not deluded, Bex,’ she snaps, walking on ahead, but a part of her wants to know more.

‘It only affects you when you see someone with your eyes,’ Bex adds, calling after her. ‘You don’t think they’re a double if you’re chatting on the phone.’

Kate stops in her tracks, turning to look at Bex. What did she just say? Kate thinks back to her conversations with Rob, how familiar and reassuring he sounds when she calls him on her mobile.

‘Really?’ she says.

Bex nods, smiling sympathetically. ‘It can be caused by lesions in the part of the brain that was damaged in your car crash.’

‘OK,’ Kate says, trying to take everything in. ‘I’m sorry, I didn’t mean—’

‘It’s fine,’ Bex says, interrupting her. ‘Maybe you should talk to Dr Varma about it. When you see him next. It might be nothing.’

It doesn’t sound like nothing. A part of her feels better already. A specific syndrome, linked to her injuries, is more reassuring than thinking that she’s gone mad. It would explain the funny feelings she has every time she sees Rob, the normality of their phone conversations.

It still doesn’t explain the jets though. She can hear one now, far out at sea. Maybe she’s imagining that one too.

Five minutes later, Kate and Bex have broken away from the main group and are searching the high-tide line in silence, scattering seabirds in front of them as they go. Jake would know their names. Ruddy turnstones, he whispers in her head.

‘Where’s Stretch gone?’ Bex asks, looking up.

‘He’ll be around somewhere,’ Kate says.