She perches on the edge of the office chair and stares intently at the picture, her heart racing as she looks for clues: how to tell when your boyfriend’s been replaced by a double.

She stays like that for a long time, holding the picture in front of her as she tries to recall some of the tricks and techniques from her old police job. Gait, facial features, tells – she knew about them all once. Her boss even sent her on a behavioural analysis course. She reminds herself that she was pretty good at recognising people, one of the best. She was never wrong.

So what is it with Rob that’s different?

She replays the details of her recent funny turns as dispassionately as she can. Something about him has definitely changed. It’s hard to describe, but it’s almost as if he’s impersonating himself, over-emphasising the little tics, the blinking eyes, the hand through his hair. Physically he looks identical, but there’s something about him – is it his blue eyes, what they’re hiding? – that doesn’t sit right with her.

She props the picture back against the wall, walks over to a row of bookshelves and glances at some of the titles. Most are to do with business investment. Some are about coding, others are about health, neurotechnology and bio-engineering. There are several books about consciousness, exploring the twilight zone between life and death, another about locked-in syndrome. And on the bottom shelf a row of paperbacks. She bends down and pulls one out. It’s an old, well-thumbed book by Fyodor Dostoevsky: The Double. She reads the blurb on the back, returns it to the shelf and pulls out another faded paperback: The Private Memoirs and Confessions of a Justified Sinner by James Hogg. Written in 1824, it’s about a Gothic double.

She doesn’t know what to think about all this doppelgänger stuff. Rob is clearly more obsessed with it than she realised. So obsessed that he keeps it under lock and key.

That doesn’t mean he’s been replaced by one. Of course he hasn’t. Bex was right to call her out on that. A double would have to look identical, imitate Rob’s mannerisms, perfect the way he talks. He would have to learn everything about Rob’s history, about her…

She pushes the thought away. She’s just being silly again. She also feels – unreasonably, perhaps – a little misled about the storeroom that isn’t. It’s a full-blown office, full of Rob’s things. Maybe he does work in here, when she’s asleep, which is often.