The summer was long and reminded everyone of global warming and no-one knew how to enjoy it. Lucy saw a small boy releasing water from a tap in St James’s park, his big yellow dog lapping at it. All across the city, galleries were full. Irritated couples and young parents with strollers prickled in agitation that others had the same idea about using the cool spaces inside the National Portrait Gallery and the Tate as respite from the heat. Exhibitions were at capacity but people let out soft sighs like they were turning over in bed and no-one really paid attention to the things on the walls.

Then, it was winter. Evenings arrived early and the nights were cold. London in December, one Friday afternoon. Lucy stood at the bench examining images of the lower jaw of her young patient, while the girl spat water into the yellowed sink. Her mother dashed up to Lucy. She stood beside her, throbbing with panic.

‘I don’t want her to have a big, risky anaesthetic.’ Mrs Paulson had wild dark hair and eyes to match.

‘Well,’ Lucy said, ‘I’m not keen on pulling out a child’s entire set of teeth without pain relief.’ Four years old and with twenty teeth that needed extracting because Mrs Paulson still breastfed her through the night. Lucy forced a smile.

For the rest of the day, Lucy tried to suppress her judgement. But she marvelled at the woman’s carelessness. She sent the paperwork out to Genevieve, the clinic’s nurse, underlining a significant discount to get the whole thing sorted. If Mrs Paulson didn’t want Lucy to do it, Genevieve could suggest other clinics, some with qualified dentists, but none without risk. Lucy treated four more patients, two of whom asked, not without dignity, if they could pay another time.

She made a cup of tea. She remembered the strange message from last night that she hadn’t yet answered but pushed the thought away. She unboxed rows of extracting forceps in crackling sterile packages and slim boxes of mirrors, stowing the rubbish in the clinic’s 300-litre aquarium that had once kept tropical fish. She tried to scrub the sink clean.

Icy air and sharp wind – evidence of the season, no matter how short – hit Lucy and Genevieve outside the clinic at five o’clock. On Mondays, Wednesdays and Fridays, the city switched on the streetlights. Today, soft globes of light glowed along the darkening street. Lucy buttoned her coat and waved goodbye, then, remembering, turned on her heel and doubled back to see if Genevieve had rebooked the Paulson girl. Genevieve palmed her cheek, annoyed with herself; she’d do it first thing Monday.

Lucy headed for home, where she dropped her bag on the bedroom floor and went into the tiny bathroom, and took off her coat, then her cardigan, then unbuttoned her shirt, then shed her bra and searched out the lump in her left breast with the fingers of her right hand. All day she worked on people’s teeth, attended to their worries. For hour upon hour, her mind tamped down on others’ pain. But in the lulls between patients she met herself in the mirror of the old clinic and her mind dilated with despair, remembering the corrupted cells incubating under her skin.

*

On Saturday afternoon, the heating having run out, Lucy was finally warm in bed under the covers. Outside, the day was almost finished, the sky fox-burnished.

She rolled over and reached for her phone. The message. Unanswered. It was from a man she didn’t know: Jay was a fan of her father’s work, he said. He loved everything her father had ever designed or helped construct. With life as grim as it was nowadays, with people lonelier than ever, he’d love to convey to Lucy how much her father’s ideas meant to him. Would Lucy meet him at the Garden Bridge?

She lay staring at the ceiling, holding her phone to her chest.

She supposed Jay had found her name in the regular way. Six months ago, a reporter called to ask for comment, before the Guardian published her father’s obituary. The article labelled him a maverick, quoting those who said he was a genius, others who called him single-minded in all respects, hinting at arrogance. He never expressed publicly any regret for the Garden Bridge and what happened there.

Twenty years before that, The New Yorker ran a story after the money had finally been raised for a taller, grander version of the original design, financed almost entirely by a hyperactive billionaire who, Lucy’s father said, couldn’t tell the difference between a birch and an oak. Wind farms were an eyesore, the billionaire said more than once. But a bridge with trees would be a monument.

Construction got underway. By that stage, public opinion was no more favourable than when the idea was first floated at the start of the century. But the project would go ahead.

Lucy accompanied her father to the opening, which was on a Saturday in spring. Creamy clouds were torn in the sky. Scents from pelargoniums in their planters and swarms of snowy hawthorn stung the air. Lucy saw women in bright dresses, handsome men in pale blue shirts open at the neck. These were the celebrities who walked up and over the bridge first, holding her father’s arm. Politicians disappeared among the foliage ahead. Investors frolicked behind trees.

Then, when Lucy was in high school, there was an accident. Later, she found out about the calls for better pedestrian management during peak tourist season to reduce congestion at the entrances. But these had been ignored. There was a crush and two people died – one of them a child. After the bridge reopened, others came, usually at night, so many until it seemed a single line of bodies converged on a spot in the centre of the bridge, where it was thirty metres wide and at its greatest distance from the water. Low hanging branches worked to camouflage people’s intent. Here, people pressed themselves against the edge like tongues, numb with pain, right before they plummeted. Of all the things that were prohibited, like sprinting and cycling and skateboarding and drinking and releasing ashes and riding a horse and flying a kite, the most dangerous activity was the one that couldn’t be banned, the one it became notorious for. Never prohibited because that would have been impossible to predict. The city could close the bridge but, short of pulling the whole thing down, it would remain. A three-metre high palisade fence was erected at both ends. The rate of deaths slowed but never stopped.

Now the trees at the centre were overgrown and loveless. The flowers in their long planters fought and won against neglect and continued to flourish among the weeds.

Eyes shut. A sensation of plunging, falling. Lucy opened her eyes and sat up in bed. Above her, lined up on her bed head, stood a photograph of her father seated at his studio desk, and three small pot plants. The leaves of a rabbit’s foot fern touched her on the arm. Lucy thought of the garden from her childhood house, which was filled with hawthorn trees. She remembered autumns home from school, lying beside the fireplace tipping her toes in her father’s lap. He liked to balance a glass of whiskey on the arm of the sofa.

She examined the pilling on the seams of her red woollen gloves. Okay, she wrote, four o’clock Sunday. Temple entrance.

On Sunday afternoon at Temple station, Lucy considered the sanity of coming alone to meet a stranger. She stepped out of the Underground. After two days at home by herself, being out felt abrasive. She dug her gloved hands into her coat pockets. Sometimes, she found herself in public pressing her palms to her breasts. Remembering the lump was an action like treachery – her own body directing her attention to something that would cause her pain to think about. Her feelings towards her body were deeply complicated. The prayer she tossed through her brain while she touched herself at the mirror wasn’t Let me live but Go back in time. Pinpoint the moment the tainted cells took hold and simply Change that day.

Commuters hurried past the pigeon-grey wall of the tube station, heads down against the cold, bodies compact. For three or four seconds she held eye contact with a man – black hair, clean-shaven, short and powerful, eyes like liquorice – wearing a backpack and a brown jacket. And just as naturally as if they’d already met, she raised an arm and waved. It was Jay. They didn’t shake hands but he motioned for her to cross the road. They took up a spot at the handrail beside the palisade fence.

The bridge should have been beautiful and for a time it was. Now, Lucy noticed a pair of boxy CCTV cameras peering down from the spiked top of the fence. The phone number for a suicide hotline was printed on a sign bolted at one end, and beside it, not quite blocking the space where the walkway had once been, stood an overflowing concrete bin as big as a barrel. Packets, paper cups and slimy twists of paper were dammed up against the base of the fence. At night, the river reflected the safety lights; people on houseboats saw the lights strung above as they passed underneath. Some days, in late afternoon sun, the bridge ghosted in the windows of buildings and in buses driving by but people’s eyes skimmed right past.

‘This must be a difficult place for you,’ Jay said. He clasped his hands, which were shaking. Lucy looked past him to the hanging garden. Thin coils of branches snaked to the ground.

She thought of a noose.

The truth dropped into her mind like a stone. ‘You’re not a fan of my father’s work.’ She felt short of breath, ill, as she stared at the water below. ‘That isn’t why you contacted me.’

‘No. I’m not a fan.’

Lucy shut her eyes and felt the handrail’s smooth iciness.

Had she been waiting for Jay or, if not him, someone like him? Perhaps a red-raw, rain-soaked father of one of the victims – the child was Venezuelan, only eight when she died while on holiday, visiting her aunt and uncle. Photographs showed her cute and chubby in t-shirt and skirt, hair braided. Her family’s sadness must have been immense.

A knock on her door like that – well, she expected it. She would be open to his reprimands, to the way she imagined a man from Venezuela would behave – Lucy was shameless in how narrowly she pictured this foreigner, dark and large with anger. She’d let him take her in his teeth, his grief so wide and starving.

The other victim was a pale blonde artist, all cherry lips and resin earrings, the mother of a small son. In the crush, she had suffocated.

‘Who did you know?’

‘My brother.’

By that stage, her father had moved on to new projects. He hadn’t spoken about the bridge for years. When the inquest report was released, Lucy read it online, hungrily. She looked up from the final page, remembering the trip to a village in Sweden when she was five or six. They crossed a bridge covered in flowers. Lucy skipped over it. Her father remained in the middle. He was the pivot point, while she passed back and forth, while he made plans and visions in his mind.

A knock at the door. Let them in, the victims’ families. They would glimpse the charcoal print in the hallway and her gumboots against the wall. A knock to dislodge the guilt.

‘How old was he?’

‘Nineteen.’

She breathed deeply. ‘He could have done it on any bridge.’ All her good intentions evaporating. The spectre of the Venezuelan father winking out. She felt, unaccountably, defensive. This shaking man beside her, his intimate agitation.

‘Yes.’

‘He could have been hit by a bus or died snorkelling off a reef somewhere,’ she said. ‘Or an overdose. In Ibiza. Do people still go there?’

‘He could have.’

‘When did it happen?’ Without knowing why, she hoped it was recent.

He let out a moan, almost unnoticeable. ‘Just over a year ago.’

The wind threw itself against Lucy’s face. It stung her cheeks. The Thames was silver and creased in countless places. A low-slung yacht scooped along the water as Jay reached into his pocket. A gun. Of course. Remarkable how much she didn’t mind. Only a little fear existed inside her. Life was different now. The city was different from when Lucy was a girl. And being part of it meant letting go of old ideas about how long you got to live.

But instead, Jay brought out a cigarette. Lucy was surprised to feel relieved. He offered her one, which she declined. He cupped his hands, sparked the flint and waited for the flame to catch. It was old-fashioned, red plastic with a half-chipped off logo. Coca-Cola? Most of these lighters had been banned, along with plastic toothbrushes and thousands of other objects that transformed into depressingly sturdy vessels that pitched on waves and sieved down the gullets of humpbacks.

The list of things she missed was incredibly long; toothbrushes were almost nothing. She’d been a child at boarding school before the worst of it happened. Memories of the extravagance, but also the simplicity: bowls of cream, pyramids of scones, platters of thick pink fish, three different types of rice. Papaya and oranges so plentiful the girls arranged slices into patterns on plates to pass the time at dinner before sweeping the fruit into the bin. She remembered it all with shame and hunger.

Jay smoked, bowing his head towards the water. These days, he told her, he smoked and meditated. The trick with meditating was to realise the brain could be treated like a muscle that responded to training and repetition. Returning to the void was the challenge. Meditation would save him, he joked. He exercised as much as possible and tried to limit his worries. He would live for decades, perhaps. It was a cheery thing to say but Jay didn’t seem cheerful. When he turned his face up to her, he grinned, showing perfect white teeth. She thought of the Paulson girl, the rot she had inherited.

‘Nobody needed it,’ Jay said. ‘This should never have been built.’

He told her that boys from their neighbourhood assumed he and his brother, Dima, were rich.

Dima’s Russian name, their father’s slick black hair.

‘Dima liked to pretend a lot. His whole life. He could have been anything,’ Jay said. ‘When we were kids, he loved breaking things apart, looking inside, rebuilding it from scratch, showing the others. But a different product at the end. A computer changed. A battery made smaller.’

Jay stubbed out the cigarette, swung his backpack around and unzipped its mouth. Opened the bag. A dark cavity.

‘What—,’ she started.

But then Lucy saw: something homemade, something deadly, that would have impressed those neighbourhood boys. ‘Whatever happens,’ he said. ‘they won’t rebuild it.’

She imagined the phone calls this time – from newspapers and radio stations, catching her live on air. She was terrified of it all. Nothing felt safe anymore.

‘I wanted to give you one last chance to see it,’ he said, not touching the explosives.

*

She would go to Sweden.

In the kitchen of her flat, Lucy filled a can and watered the row of African violets on her bedroom window sill. Perhaps if she didn’t return, a person walking on the street below would notice them flourishing.

She left, taking very little. She paused outside, keys in hand, when a moment of nostalgia ballooned inside her. But she hadn’t lived there for long – less than a year – and the nostalgia subsided. She shouldered her duffel bag. Inside it were a pair of trainers, jumpers, jeans, underwear, toiletries, a book of her father’s. She locked the door.

Yes, toffee-coloured, sweet-boxed Stockholm would do. Lucy yearned for a place other than London’s unlit lanes and whiffy air, the grimy pavements and sour people who were tetchy with panic and oftentimes hunger. Some days she could barely see the lid of the sky. Too much pain at the clinic, too much drudgery and uncertainty to ruminate on each night. The promise of this new destination was now a bridge of a different sort, a tremendous light-filled opportunity. Less her father’s failed garden path connecting two halves of a divided city than an elegant suspension bridge spanning a before and an after – a slender piece of steel. She didn’t know if it would hold, if such a thing were possible. But the challenge would have tempted her father.

Now, possibilities trod through her like footfalls. She reached out to this future, however long it would last, in whatever form her body took.

At St Pancras, Lucy paused at a screen showing CCTV pictures. She’d last glimpsed Jay by the tall fence, a shadow gaining a foothold. Investigators were searching for this man – here, his frozen black-and-white image – as well as a woman with long brown hair, seen talking with him before the attack. The chaos of aerial footage of police cars hastily parked. Lucy saw a bite taken out of the belly of the corrupted bridge. A dark space existed now where Jay’s bomb must have exploded, looking like a door through which a man might disappear, and then his brother, and then a woman after them.