Elina hands him the baby and watches as Simmy sits him on his knee. 'Hello,' Simmy says solemnly. 'Did you have a good lunch? Milk again, was it?' Jonah stares at him, entranced.

Elina stands, swings her arms up and above her head. She glances down the harbour. No Ted. She glances back at the bench, where she sees a waiting package of sandwiches. Ted's. Elina steps away from the bench to look up the harbour towards the curve. Nothing. Where can he have got to? Elina runs up the narrow, jutting steps to the top of the wall and finds herself on a higher level, a sloping stone surface that tilts sickeningly towards the sea. She holds her hair out of her eyes and looks about her.

'Can you see him?' Simmy says from below.

'No.'

And then suddenly she can. He is coming around the curve of the grey wall. He must have been out to the end. Something about the way he is moving alerts her. The left arm clutched in the other. The bowed head. The stumbling, uneven walk. Elina moves forward on the tilting stones. She raises her hand to wave. But Ted turns away from her. He looks down into the sea, which swells and recedes just below him, and the thought crosses her mind that he is about to jump in, but then Ted never swims, she doesn't even know if he can he hates the idea, he always says, why would anyone want to do that? She sees him rear back from the water and then he falls. Or stumbles. Or perhaps collapses. She isn't sure which.

Elina shouts his name but the wind snatches away the sound. She breaks into a run but she is a whole level above him and she can't find a way down and when she does find another stone staircase it is worn and vertiginous and she must be careful not to trip and fall. When she gets to Ted, there is a crowd of people already around him. Simmy is there, with Jonah held in his arms Elina can see his back in its striped shirt. He is crouched over, with his ear to Ted's chest. People in the crowd must see her significance or her panic because they stand aside to let her through, and when she reaches him, she kneels on the wet stone beside him and takes his hand; she strokes his hair, she talks to him in Finnish and then in English, and when the ambulance comes, she gets in beside him, still holding his hand.

There follows a great deal of waiting. There are forms to fill in. They are asked to move from corridor to corridor. And a number of people ask Elina the same questions, over and over again. What's Ted's age? Where does he live? What's his full name? Has he taken anything? Does he use drugs? Is there a history in his family of heart problems, diabetes, low blood pressure? Has this ever happened before? No, Elina says, and no, no drugs, no medication, Roffe, Ted Roffe, Theodore Roffe. Someone brings her a cup of tea and, later, someone gets her some spare nappies for Jonah. Thank you, Elina finds she keeps saying, thank you, thanks.

She and Simmy wait in a corridor. Jonah fidgets and cries and feeds again. He is sick, copiously yet matter-of-factly, all over the next chair. He grabs handfuls of Elina's hair, sucks it crossly, then investigates the fastenings of Simmy's jacket. He seems baffled, impatient about this unusual turn of events, as if he can't understand why they have taken him away from the seaside to sit in these featureless beige corridors. Elina bounces him up and down rhythmically on her knee; Jonah holds his legs stiff and Elina imagines all the small black bruises that will cover her thighs tomorrow.

Then there is a flurry of doctors and student doctors and nurses coming to talk to them and the news, they say, is good. It's good! Simmy is leaping up and he is smiling. It wasn't a heart-attack after all! They are all striding along the corridor now and several people are talking at once. The word 'eeceegee' is mentioned and Elina has no idea what it means but Simmy is nodding and still smiling, and the words 'clear' and 'tested negative'. As they enter a room, the doctor is saying 'a form of panic-attack' but Elina isn't listening because Ted is there on the bed and he is dressed and he looks normal again.

Elina rushes over to him, puts her hand on his arm, kisses his cheek and, as she does so, Jonah gives a painful yank to her hair so that she cries out, 'Ow,' just as her lips touch his skin.

Ted's face is filled with alarm. 'What's the matter?' he says, cringing away from her.

'Nothing. Sorry.'

'Why did you say that, then?'

'Jonah just pulled my hair. It's nothing. How are you feeling?'

Ted continues to stare at her. And Elina sees that his face is white, his pupils wide and black. He moves his gaze and stares at Jonah. Then back to her. Elina glances at Simmy, who is looking carefully at Ted.

'Umm,' she says. 'Do you feel OK now? Ted?'

Ted looks at his son again. Then he lies back on the pillows behind him and stares up at the ceiling. He puts both hands over his face. 'Do I feel OK?' he repeats, inside the tent of his hands, very slowly. 'Do I feel OK?'

Simmy clears his throat. 'The doctor said you can go but if you think-'

'I don't know,' Ted intones. 'Is the answer.'

Simmy and Elina exchange a glance over Ted's body. Jonah huffs on the skin of her neck, sucks briefly on her collarbone, drags up a fistful of her dress to taste, arches back in her arms to examine the ceiling, kicks his legs against her abdomen.

'I'm just going to find a loo,' Simmy says. 'Be back in a sec.'

And then they are alone, Elina, her man and her baby. It seems incredible to her that Ted has been delivered back to her, after she had seen him fall on the harbour, after his body was crumpled like that on the ground, crumpled and horribly twitching. It seems nothing short of a miracle that they should have come through such a thing and found themselves here, in an empty hospital room with striped sheets. Elina stares at the stripes, which seem, like everything else at this precise moment, magical. The way they alternate, white, blue, white, blue, the weft and warp of the cotton meshing together to make this. A sheet. For Ted to lie upon.

Elina sits herself on the bed next to him, her hip pressed against his. 'You scared me so much,' she murmurs. Jonah leaps and writhes like a fish in her arms and she has to hold tight to his ribcage. 'The doctor said you must go and see the GP as soon as we get back h-'

'The thing is,' Ted interrupts, still staring at the ceiling, 'none of it adds up. I just know that everyone's been lying. About everything. I see that now. And I don't know where to turn, who to ask because everything is deception, and I can't trust anyone. Do you see?' He looks at her or near her or through her. 'Do you see that?'

Jonah twists in her hands, stamping his feet on her legs. Elina can feel her arms trembling, her whole body trembling. She has no idea what to say, no idea what to do. She wonders if she should call a doctor, but what will happen then? What is happening to them?

' Ted,' she gets out, and her voice cracks, as if she might cry, 'what are you talking ab-'

'Right.' Simmy has re-entered the room, rubbing his hands together. 'The doctor says we can go. Shall we make a move?'

'Sim,' Elina says, but Ted is leaping from the bed.

'Come on,' he says, seizing Elina by the elbow and dragging her towards the door. 'Let's go.'

'I think we should wait and see if-'

'We have to go,' Ted says, shoving his way out. 'We have to get back to London.'

This is where the story ends.

Lexie became what she is today during a swim off the Dorset coast in late August. She and Theo are with Robert in Lyme Regis. They have eaten fish and chips, they have talked about the hotel they stayed in when they last met, they have argued about an article of Lexie's that Robert read recently, Theo has filled a bucket with stones, he has found a dead crab, and Lexie has stripped off her clothes and swum. Robert has watched her, holding the towel for her, waiting. Like the husband of a selkie, Lexie thinks. She watches them both from the water, Robert sitting on the steep shingle, the buggy parked next to him, in which Theo sleeps, knitted cat clutched in his hand.

When Lexie gets out of the sea, walking carefully because the beach is pebbled and sharp, and Robert puts the towel around her, she knows that she has to be in bed with him in the next few minutes. It is a necessity to her and life itself. He is rubbing her under the towel, his palms moving up and down her back, her arms, her hips.

'The hotel,' Lexie says, her lips rubbery and strange with cold, 'let's go.'

And Robert just says: 'Yes.'

She loves him for that yes, for the way he turns to pick up their bags, for the way he strings her discarded clothes over his arm, one by one, the way he bends to unlace the shoes she'd kicked off in her impatience to be in the water, and helps her on with them so that she can dash, with him carrying the buggy and the napping Theo, up the concrete steps to the promenade, up the hotel steps, past the shocked face of the manager, up the four flights of stairs, and her in only a bikini and towel.

The way he turns the buggy towards the wall. The way he rips off, first the bedcovers, then his shirt, then her towel. She likes the ordering of that. The way his skin seems scalding hot against the chill of her own. The way he struggles to unwind her from the clinging, winding straps and catches of her wet bikini, swearing with impatience, until she does it for him. The way he seizes the damp bundle from her and hurls it at the wall. A shadow on the plaster will be there afterwards and for the rest of their stay, in the shape of a jellyfish, and later guests will look at it and ask themselves what could have made such a strange stain.

She loves him for all these things, and for the paradox of his body the hardness of it under the softness of the skin and for the line of hair that runs down his stomach, which she had forgotten was there. For the intent, concentrated way he encounters her, for the expression of utmost seriousness on his face, for the feel of him inside her, at last, and after such a long time.

Afterwards, he falls asleep. Lexie does not. She stretches, yawns, gets out of bed. She picks up her dress and pulls it on. She goes over to Theo, still slumped in his buggy, eyes moving beneath the lids, lips pouting in sleep. She watches him for a while. She watches him and touches his hair. One of his hands is loosely uncurled on his lap and she spends a while looking at the hundreds of tiny lines crisscrossing his palm.

She wanders to the open window. On the promenade below, people are eating ice-cream, leaning on the railings, walking up and down. The tide has come in since they were on the beach: its frothed waves lap and lick at the promenade wall. An old man is letting his dog pee against a statue. A small child skips out of a shop with an armful of oranges. It amuses Lexie that everyone is going about their business while she, a woman in a dress at a window, can secretly look down on them.

She is thinking about where they might eat later, about when Theo might wake up, about whether he might like to fly a kite she's seen a red one with a yellow tail in a shop she might get him. She is looking at the great grey Cobb, lying like a sleeping serpent, half out of the sea.

A movement from the buggy makes her turn. She crosses the room. Theo is waking up, twisting his head from side to side. She turns the buggy around and crouches in front of him. 'Hi,' she whispers.

He yawns and then says, quite precisely, with his eyes still shut, 'I said I didn't want it.'

'Did you?'

'Yes.' Then he frowns and blinks and looks around him. 'This isn't home.'

'No. We're in Lyme Regis, remember? In a hotel. You've had a little nap.'

'Regis,' Theo repeats, then his face seems to tense with a thought. 'A . . . a bucket with stones.'

'That's right. It's over there, look.'

He stretches and then pushes himself out of the buggy, tucking his knitted cat up under his arm. 'Alfie doesn't like Regis,' he states, as he goes towards the bucket, which Lexie has left beside the door.

'Doesn't he?'

Theo leans over the bucket and examines it carefully. 'No,' he says.

'Why not?'

Theo has to think for a moment. 'He says it's too damp.'

Lexie, sitting on the edge of the bed, tries not to smile. 'Well, he is a cat. Cats hate the wet.'

'No, not wet. Damp.'

'Damp is wet, darling.'

'No, it's not!'

'OK.' She bites her lip. 'Would you like a drink?'

Theo is lining up the stones in a row, taking them one by one out of the bucket. The grey ones, she notices, he discards.

'Theo?' she tries again. 'A drink?'

He places a smooth white stone next to an orange one. 'Yes,' he says, distant but firm. 'In fact, I would.'

Later, they go out again. Lexie buys the red kite with a yellow tail and they go to the beach beyond the town, beyond the Cobb. Theo holds the string in his hand and Lexie puts her hand around his. Robert watches them from a rock where he is searching for fossils.

'That's it,' she murmurs to Theo. 'You've got it.'

The kite floats directly above them, an inverted plumbline, its tail swirling and snapping. Theo gazes up at it, rapt, unable to believe that when he jerks his hand this ethereal thing above them will dance in response.

'It's like . . .'he struggles to find what he wants to say '. . . a dog.'

'A dog?'

'A . . . a floating dog.'

'Oh, like on a lead, you mean?'

He turns his blue eyes to hers, in joy, in delight at being understood. 'Yes!'

She laughs and hugs his body to her and the kite above them dips and sways.

After a while they join Robert and sit together on a rock. Robert finds an ammonite, a ridged creature, curled into itself, petrified into rock. He puts it in Lexie's hand and she feels it begin to warm in her palm. Theo is lining up stones again, this time in diminishing size order.

Lexie stands. 'I might go for another quick swim. And then we'll find something to eat.'

Robert looks at the sky, at the sea, which is flecked with white horses. 'Are you sure?' he says. 'It's getting cold.'

'It's fine.' She slips the ammonite into her dress pocket.

'We haven't got a towel.'

'I'll dry,' she says, laughing. 'I'm waterproof. I'll run around until I'm warm.' When she's down to her underwear, she crouches to kiss Theo on top of his head. 'I won't be long, sweetheart.' And then she's off, down the shingle, on to the sand, into the water. Robert watches as more and more of her disappears into the sea it claims her quickly. Her ankles, her knees, her thighs, her waist. Then she's in, with a small cry. He watches as she does a few strokes of crawl, the water churning in her wake; he watches her dive under, sees her slick head break the surface, further out now, and then she glides into an even breaststroke.

Robert looks back to Theo. He is pushing the stones, one by one, into the sand, saying, 'There you go,' with each one. 'There you go, there you go.'

It will be unclear to Robert, later, how much time passes here. He knows that he started looking again, idly, for fossils. He knows he took a few stones and hammered them against rocks, to crack them open like eggs, to see if their innards revealed anything. He knows he looked out to sea at least once and saw her head, near the curve of the Cobb. He knows he listened to Theo, saying, there you go and, occasionally, she'll run around until she's warm.

After cracking open the third stone, he hears Theo say something else. Robert looks up. Theo is no longer crouched over his stones. He is standing up, his sandy hands held away from his body, fingers splayed, staring out to sea.

'What did you say, Theo?'

'Where's Mama?' the child asks, in his clear, high voice.

Robert is weighing a fourth stone in his hand, considering it, examining it will it yield another perfect ammonite, like the one he gave Lexie? 'She's gone for a swim,' he says. 'She'll be back soon.'

'Where's Mama?' he says again.

Robert looks out to sea. He looks left, towards the Cobb, he looks right. He straightens up. He follows the charcoal line of the horizon. Nothing. He shades his eyes against the dull glare of the setting sun. 'She's . . .' he begins. Then he walks towards the shore. Waves rise and collapse against the sand. He scans the sea stretched before him.

He sprints back up the beach towards the child, who is still standing, fixed to the spot, his hands covered with sand. Robert picks him up and hurries over the shingle. 'We'll go up to the Cobb and look from there, shall we?' he says, and the words come out not as he'd hoped, reassuring and calm, but ragged and panicked. 'She might have swum round the end and be coming down the other side.'

Robert climbs the steps on to the Cobb's high wall. He races along the sloped stones, Theo clutched in his arms. Halfway along, he comes to a stop.

'Where's Mama?' Theo says again.

'She's . . .' Robert looks. He looks and looks. His eyes ache with looking. He cannot remember ever seeing anything other than sea, endless, puckered water, unbroken. Every few seconds, his heart leaps at something a buoy, a particularly peaked wave. But there is nothing. She is nowhere.

He scrambles down off the wall, to the lower part of the Cobb, and runs towards its end. The water here is deep, sinister green, dipping and snatching at the wall. Theo begins to cry. 'I don't like it,' he says. 'That sea is too close. That sea there.' He points at it, in case Robert hasn't understood.

Robert turns, rushes back along the wet Cobb as carefully as he can, to where several fishing-boats are moored. In one of them a man is standing, his arms full of knotted nets.

'Please,' Robert calls down to him. 'Please. We need help.'

Then there is a long stretch of time when Robert is sitting on a bench on the Cobb, with Theo in his arms. Beams from the lights of trawlers, the lifeboats, the coastguard sweep over them from time to time. He has wrapped the child in his coat. Only his hair is visible. Theo shivers rhythmically, gently, like an engine in low gear. Robert rocks him back and forth, sings a song he used to sing to his own children a long time ago, his voice cracked and hoarse. Someone he doesn't see who, one of the policemen, perhaps brings a woven bag and places it next to him. He doesn't recognise it for a moment. At the top of the bag is a loosely folded piece of fabric. Then he sees that it is Lexie's dress, Lexie's bag, that someone has collected them from where they were sitting on the beach. Without letting go of Theo, he picks up the dress. It unfolds in his fingers like something sentient, like something alive. He almost drops it but doesn't, and then he is puzzled by the weight of it. How can something of thin cotton be so heavy? It swings back and forth like a pendulum in the stiff breeze. Then he remembers the ammonite. She put it into her pocket just before- He puts the dress down quickly, stuffs it back into the bag. And then he sees the toy Theo loves, the stuffed cat, among a tangle of beakers, spare shorts, buckets and spades, a green rake. He lifts it out, places its nonplussed face at the gap in the top of his coat, where Theo's bright, golden hair can be seen. For a moment nothing happens. Then fingers appear, clutch at the cat and pull it down inside the cave of the coat.

And then two policemen are running down the brow of the Cobb towards the dock. The other police, seeing them, start moving too. Robert stands, hoisting Theo up. He hears someone mutter, 'They've got her.'

And he is moving forward. A boat is rounding the tip of the Cobb, a small trawler, its lights blazing, a man at the helm and another standing at the stern with a rope. Robert strains his eyes and sees, unbelievably, a shape crumpled at the bottom of the boat, half covered with tarpaulin and he finds he wants to shout, to cry out to her, but then a policeman is standing between him and the docking boat and he is saying, stand back, sir, please, get back, take the child, take him away.

This is how it ends. Those words were running through her head. So this is how it ends. She knew what was coming. There was a stretch of time, out there beyond the reach of the Cobb, several minutes long, where she was flailing against the cold, muscular clutch of the current. And she saw. She saw what was coming. She knew the struggle had begun and she knew that she was losing.

She didn't think in that moment of herself, of her parents, her siblings, of Innes, the life she left behind when she stepped into the waves, the moment when she could have changed everything, when she could have stayed on the beach, turned her back on the sea. She didn't even think of Robert, who was sitting there with her clothes, who would soon be calling her name into the restless wind.

As the waves thrust her under, she could think only of Theo.

They heaved her up and heaved her under, and every now and again she could struggle to the surface, she could make the waters part so she could take a breath, but she knew, she knew it couldn't be long, and she wanted to say, please. She wanted to say, no. She wanted to say, I have a son, there is a child, this cannot happen. Because you know that no one will ever love them like you do. You know that no one will look after them like you do. You know that it's an impossibility, it's unthinkable that you could be taken away, that you will have to leave them behind.

She knew, though, that she would not see him again. She would not be helping him cut up his dinner tonight. She would not be folding the kite or airing his damp clothes or running him a bath at bedtime or taking his pyjamas out from under the pillow. She would not be rescuing his cat from the floor in the middle of the night. She would not be able to wait for him at the gate at the end of his first day at school. Or guide his hand as he learnt to shape the letters of his name, the name she'd given him. Or hold the seat of his bicycle as he did without stabilisers. She would not be nursing him through chicken pox and measles; it would not be her measuring out the medicine, or shaking down the themometer. She would not be there to show him how to look left, then right, then left again, or to tie his own shoelaces or brush his teeth or manage the zip on his cagoule, or to pair his socks after a wash or to use a telephone or to spread butter on bread, or what to do if he got lost in a shop, or how to pour milk into a cup or catch a bus home. She would not see him grow as tall as her and then taller. She would not be there when someone first broke his heart or when he first drove a car or when he went alone out into the world or when he saw, for the first time, what he would do, how he would live and with whom and where. She would not be there to knock the sand out of his shoes when he came off the beach. She would not see him again.