‘What’s with Stretch?’ he says as he slides behind the Tesla’s steering wheel.

  She hadn’t noticed, but Stretch is now curled up on the seat, head down. He was so happy a few minutes ago.

  ‘Just tired,’ she says, scooping him up as she sits in the passenger seat. His tiny legs are trembling on her lap. ‘Walked too far today, didn’t we, little one? We’re both tired.’

  Rob glances across at her and smiles. The diffident smile that had so intrigued her as she lay in hospital, wondering if her life would ever be the same again. She knows what he’s thinking. Has she just let him know that she’s too tired for their usual Friday night routine? They’ll have to see. She hasn’t felt so well this week.

  ‘Nice hair, by the way,’ he says.

  ‘Thanks.’ She’s pleased that he’s noticed. She went for an undercut earlier today, in a bid to cheer herself up, make herself feel younger.

  ‘I got you a present,’ he says, legs bouncing like a schoolboy beneath the steering wheel.

  ‘You shouldn’t have,’ she says, watching him use the sleeve of his hoodie to wipe away a smudge of dirt on the car’s large touchscreen between them. She’d meant to clean the car before he arrived. He likes things to be spotless. ‘I already have everything I need down here. Thanks to you.’

  He reaches behind the seat, pulls out a small jewellery box from his bag and passes it to her. Inside, wrapped in tissue paper, is the piece of frosted beach glass that they found last week. It’s now on a filigree silver chain. He knows she loves necklaces.

  ‘It’s gorgeous,’ she says, suddenly overcome with emotion. ‘Thank you.’

  ‘I wasn’t totally sure about the sizing.’ He stares at her neck, a look of intense concentration on his face. ‘Whether it would be too loose. I wanted it to be snug – you know, like a choker.’

  She lets him fasten it, her neck tingling at his touch, but then the clasp catches a pinch of her skin at the back and she flinches. ‘Ouch,’ she says, playfully. It might be her imagination but he seems to hesitate a moment too long before apologising.

  ‘Sorry,’ he says. ‘It’s a little tight.’

  *

  Kate glances across at Rob’s smooth, sleeping body and slips quietly out of bed, wrapping a cotton dressing gown around her as she steps out onto the terrace. It’s a warm August evening and no one can see her here. The isolated house, all glass and oak and concrete, is cut deep into the Cornish hillside and faces out to sea, which is empty tonight, apart from the winking lights of tankers moored in the distance off Falmouth.

  ‘You OK?’ Rob calls out.

  She swings around. It’s too dark in the bedroom to see him properly.

  ‘I couldn’t sleep,’ she says, turning back towards the bay, where a ribbon of moonlight has been laid across the water.

  A moment later, his arms are wrapped around her from behind. ‘Come back to bed,’ he whispers in her ear.

  She can feel him against her, a familiar swelling. She rests her hand on his smooth forearm and thinks again about the necklace he gave her earlier, his insensitive response to her squeal of pain. It still niggles.

  ‘Thank you for the present,’ she says. He must have just been tired. Hardly surprising after a long week at work and then the flight down.

  ‘Not too tight?’ he asks.

  ‘It’s perfect.’

  Back inside the bedroom, they snuggle up in the darkness. In all other respects, he’s played it well this evening. He ran her a bath with Moroccan rose oil and brought in two glasses of chilled champagne. Her exhaustion of earlier slipped away. Afterwards, he was the one who fell asleep almost instantly, like a laptop closing.

  ‘Talk to me,’ she says now, quietly. ‘Tell me about your week.’

  She still doesn’t understand exactly what Rob does in London. One of the articles she read about his meteoric career described him as a serial ‘techpreneur’, the youngest ever founder of a British ‘unicorn’ company and a pioneering champion of something called ‘direct neural interface’ technology – the interaction between brain and machine. She likes the sound of unicorns. The ‘disruptive’ tag is less appealing. He also runs a charity on the side that puts on art shows in hospitals, which is how they met.

  ‘That’s so interesting,’ she offers, filling the silence. ‘You’ve developed an app, you say, that makes women wake up in the middle of the night begging to give their man a blowjob? That’s incredible. What a smart, selfless piece of coding.’

  He nudges her playfully. And then all she can hear is the faint in and out of his breathing, and the sound of the waves below.

  Sleep soon starts to lap at her own consciousness, but something’s preventing her from dropping off. What Rob said about doubles last weekend has been on her mind all week. She hasn’t been able to forget it, his words chasing her through her days of painting and nights of restless dreams. And I’ve already met mine, a long time ago. What must it be like to actually meet your double? And when did Rob encounter his? Where? We’ve all got a double out there somewhere, watching, waiting. Shadowless. It’s revealed an unexpected side of him. A new insight.

  She turns over, her interest piqued all over again. She remembers being fascinated by identical twins in primary school. The teacher used to tell her off for staring at them in class. Maybe it was an early challenge to her powers of recognition. Spot the difference. And there was the French-exchange girl at secondary school who apparently looked just like her. That had freaked her out.

  She lies there, sleepless, her thoughts running loose and wild. What if the French girl were to suddenly come back into her life, discover her on Instagram, decide she’d like a piece of Rob… What was it he said? It’s well within the bounds of probability for all of us to be found by someone with an exact physical likeness. Would Rob be attracted to her? The woman would have a fight on her hands if she tried it on with him. Kate smiles at the ceiling. It’s a preposterous thought. But then she recalls Rob’s tone of voice, how serious he’d been, and her stomach tightens. He’ll take over my life, me, you, the house, my company, all that I’ve achieved, everything’s that’s precious to me. Imagine living with that sort of fear. And what if it became reality? She shoves the idea to the back of mind.

  Secretly, she’s thrilled that Rob has been so honest with her, admitted to such fragility. It’s a sign that he trusts her, no longer feels obliged to be the strong one all the time. She will ask him about it again when he’s unwound from London. Diplomatically, of course. Tomorrow they’ll walk the coast path and swim, have coffee at their favourite café overlooking the harbour. She starts to drift off to sleep, warmed by the prospect.

  And then she’s awake again. Her eyes spring open in the darkness, the sound of blood pulsing in her ears. Rob always insists that he sleep on the right side of the bed. He’s a creature of habit, of quotidian routine. Tonight he’s lying on the left. Should she prod him? Check he’s not been replaced by his double? Relax. She’s being silly. It’s just another sign that Rob’s loosening up, going with the flow a bit more. She rolls over, searching for sleep again. He might be helping her to recover, but she’s doing him some good too.

  Saturday

  3

  Kate

  Kate’s up early the next morning, trying to paint Stretch on his bed. It’s not easy as he follows her every time she walks over to the sideboard to make a tea. She loves this room, a vast atrium of a kitchen, one end of which she uses as a studio. The room doesn’t face north, but there’s so much glass that it feels like she’s painting en plein air.

  The sea below the house is as still as a millpond this morning, like a painting, streaked with cyans and ceruleans and framed by a high cirrus sky. In the distance, Gull Rock stands sentinel off Nare Head, the headland where she walks with Stretch, who loves to dart along the hidden paths between the yellow-flowering gorse.

  Rob will be back soon, answering emails, making calls. No boundaries, never stops. She’s a fine one to talk, trying to paint on a Saturday morning.

  ‘It’s just not happening, weenie toes,’ she says to Stretch, who lifts his head from his bed at the sound of her voice. She puts her brush down and clutches her mug of tea, studying the canvas, trying not to panic. It will come back. Rob is certain.

  She picks up the canvas to show to Stretch. ‘What do you reckon? Can you see yourself?’ She moves the picture around like a hairdresser with a mirror. ‘No? More like a guinea pig, you think? A piglet?’

  She looks at the canvas again and places it back on the easel. ‘I see what you mean,’ she says, throwing a snort in his direction.

  She used to paint a lot of dogs before she became a super recogniser. Not by choice. When the portrait commissions dried up, she had no option. Labradors mainly. The occasional retriever. A few racehorses too. The price she paid for living in Wiltshire. Now, it seems, she can’t even do dogs.

  ‘Hockney painted forty-five pictures of his dachshunds,’ a soft Irish voice says behind her.

  She spins around to see Rob leaning against the bedroom doorway to her left, a tennis racquet in one hand.

  ‘Took him a long while to get it right. Easels all over the house, apparently,’ he adds.

  Rob practises with a machine when he’s down here, out on the court at the rear of the house. Two hundred balls on his backhand before breakfast. He peels off an electronic bandana, no doubt another piece of wearable technology he’s testing. Kate takes in his sweaty smile, his windblown, tousled hair. Something’s wrong. He folds his arms approvingly, glancing out to sea and then back at her, before looking at his trainers. He usually does that when he’s trying to get her into bed. One moment pleading, the next all bashful. But then he fixes her in the eye.

  ‘I know it’s taken time,’ he says, ‘but you’re looking so much better, Kate. And that necklace – it really suits you.’

  The necklace. She raises a hand to touch it, remembering the pinch of pain, and time seems to slow down. She stares at him, his familiar face, his blinking puppy eyes, but she no longer recognises him. Her brain tingles, like déjà vu, but this is different, the opposite feeling. It’s as if she’s never seen this man before.

  ‘Kate?’ he says. His voice is far away, distorted. ‘You OK?’

  She can feel the mug slipping through her fingers, but she can’t do anything about it. It falls and shatters on the concrete floor, splashing tea over her bare toes. Stretch trots off to another room.

  ‘Are you hurt?’ he asks, rushing forward, his hands on her shoulders as he kicks away a jagged shard of mug from her feet.

  She shakes her head slowly, still staring at him, reality fracturing around her. Rob holds her close but it only makes things worse. Who is this person? She feels disorientated, nauseous, disconnected – from Rob, the house, her life, as if she’s suddenly watching herself from a distance.

  ‘You’ve been overdoing it, that’s all,’ Rob says, glancing at the canvas. ‘When did you get up?’

  ‘Just after you went out,’ she manages to say. What’s wrong with her?

  ‘You mustn’t push it,’ he says, leading her through to the bedroom, where he closes the curtains and switches off the light. She’s suffering from a migraine, he thinks, and needs to rest in darkness. She had a lot of headaches in the immediate aftermath of the accident, but none recently.

  Once she’s settled in bed and he’s brought her a mug of herbal tea, he sits by her feet, one hand resting on her legs as he goes through emails and messages on his phone. Normality starts to return. Is this how it’s going to be from now on? Irrational, late-night thoughts about doppelgängers? Weirdness creeping up on her when she least expects it, reminding her that she’ll never be fully herself again?

  ‘I’m sorry,’ she says. ‘The painting – it’s just taking so long to come back.’

  But she can’t help worrying that it’s something else. The feeling when she saw him in the kitchen and thought he was a different person – it was so strange, sickening. The world seemed to split in two. Rob looked the same, but something – her instincts? her old self? her imagination? – was telling her that it wasn’t him.

  ‘Patience,’ he says, leaning over to kiss her.

  Rob loves her work and is determined that she’ll be a fulltime artist again. He knows that she never wants to return to her police job. She doesn’t want to let him down. Maybe she has been pushing it recently.

  ‘Art’s the best healer,’ he’d said that day they first met on the ward, lingering to chat at her bedside. ‘Art and technology.’

  When she was strong enough to walk down to the exhibition he’d organised in the hospital foyer, she was amazed to discover three of her own portraits on the walls. And she can’t deny that her euphoria at seeing them on display worked more wonders than any medicine. Two years earlier, she’d been let go by her own gallery, forced to take up a proper job with the police and ditch her career as an artist. It had been a while since she’d had any work shown in public.

  ‘I don’t think it’s a migraine,’ she says.

  ‘You just need to sleep.’

  She knows he’s right. But she’s not sure she can face more dreams about Rob being replaced by a stranger.

  4

  Kate

  When Kate wakes from a light sleep, Rob is still at the end of the bed in his tennis gear, checking his phone, getting up to walk around in circles, settling again. A bit like Stretch. Sometimes she thinks he has enough energy and ideas to solve all the world’s problems.

  ‘Rob…’ she says, but before he can reply, his phone rings.

  ‘You OK?’ he mouths to her, one hand over his phone. She nods and he walks out of the bedroom onto the terrace.

  Kate closes her eyes again and lies back, listening to his animated tones as he talks about an upcoming ‘IPO’ in language that she barely understands. The mindless ‘spray and pray’ of some tech venture capitalists. The need for algorithms and the human brain to work in partnership, his hopes for a new project in Brittany.

  Her name is mentioned, but his voice drops and she can’t make out exactly what he’s saying. And then she hears him again, cold and dispassionate, like she’s never heard him before, ordering someone to ‘boil the ocean’ for new customers. She guesses he has to be tough at work, not like how he is with her, but his tone is surprising. Two minutes later, he ducks back into the room and pulls out a familiar headset from a cupboard. Rob recently launched a disruptive medical start-up that makes portable headsets for assessing traumatic brain injuries. He gets her to wear one occasionally to help monitor her recovery.

  ‘There’s a problem in London,’ he says. ‘An unhappy investor.’

  ‘Do you need to go back?’ she asks.

  The thought of being on her own again is suddenly very appealing. She feels guilty, but she needs to work out what’s happening in her head, why she dropped the mug when she looked at Rob. It was a step back, to when she was first recovering down here and dizzy spells and migraines were part of her life.

  ‘I told them it would have to wait until Monday,’ he says.

  ‘Because of me?’

  ‘I can’t leave you like this,’ he says, adjusting the headset in the dim light. He explained once how it works. Apparently, it uses algorithms to compare a patient’s brain activity against normal data and then highlights any deviations.

  ‘I’m fine. Really.’ Kate ties back her hair. ‘You should go.’

  ‘Let’s just check,’ he says. ‘Peace of mind.’

  She sits up in bed, keeping her eyes firmly closed as he slides the device over her head. It looks a bit like a swimming cap, except for the matrix of colour-coded electrodes all over it. When he’s being tender like this, tucking her hair behind an ear as he adjusts the headset, she feels so loved, cared for, cherished. No pinched skin.

  She sits there in silence, like a good patient. The device is cool on her scalp.

  ‘All seems fine,’ he says after a couple of minutes. He’s reading from his smartphone, which is linked to the headset via the app his team of ‘brogrammers’ in London has designed. ‘When’s your next check-up with Dr Varma?’

  ‘Monday.’

  ‘That’s good,’ Rob says. ‘He might be down here already.’

  ‘How do you mean?’

  ‘He sometimes likes to make a weekend of his visits. Bring the family to the seaside.’

  Kate smiles at the thought. Dr Ajay Varma, a neuropsychiatrist, often talks about his family, how well his two young daughters are doing at school, his parents back in south India. He’s been overseeing her recovery since she left hospital, looking out for any lasting post-traumatic effects of the accident – mood swings, anxiety, depression. It all seems a bit unnecessary, but Rob insists, arranging and paying for his visits. She doesn’t mind as he also happens to be a really nice guy.

  ‘I’ll give him a call,’ Rob says, ‘see if he can come over this afternoon.’

  ‘Are you sure?’ Dr Varma’s never mentioned to her that he stays down here. But then she’s never asked.

  ‘It’s important. You’re doing so well. We don’t want any setbacks.’

  ‘If you say so.’

  ‘I do. And I love you.’

  ‘Rob?’ she says, eyes closed. She so wants to build on his new-found openness, get him to confide in her again, talk some more about his fear of doubles. Make things more equal between them.

  ‘Yes?’

  She takes a deep breath. It suddenly all seems too much. Her funny turn feels like a step back and he’s in carer mode again, seeing her questions as intrusive and deflecting them.

  It’ll wait. She gives him a defeated smile. ‘I love you too.’

  5

  Kate

  ‘It still doesn’t feel right,’ Rob says.