It was Mia who found it. She came across the blue and white cardboard box in one of the storage crates stacked in the garage. Strictly speaking, it was inside its packaging, inside a box that was inside the crate, a bit like the set of Russian dolls on the bookshelf in her bedroom. Whoever put this here didn’t want it to be found but neither did they want it to be lost. Later she would say it was as if it was waiting to be discovered. Later still, she would claim that it called out to her. Because how else could you explain the mysterious way the pregnancy test revealed itself amid the chaos of thousands of family belongings?

Mia pulled the plastic dipstick out of its packaging. She might be only ten years old but she had watched enough Pretty Little Liars with her older sister over the summer to understand that the blue line in the little window indicated that the person who had peed on the dipstick was going to have a baby. Her knowledge of the mechanics of sex was a muddle of what she had learnt from David Attenborough and sex education classes at school, but she knew that, strictly speaking, the thin blue line meant this person had mated and, strictly speaking, the sex had led to reproduction. ‘Strictly speaking’ was her favourite new expression that summer.

But suddenly it seemed to have vaguely sexual connotations, as did the word ‘dipstick’ and the salty taste of sweat she licked from her upper lip. She felt intoxicated, as if she’d drunk black coffee or dived into freezing cold water.

She gingerly held the pregnancy test between the tips of her thumb and index finger as if it might be contagious, which in a sense it was, although not in ways she could possibly imagine. She was half wondering if she should take it to school when the new term started. ‘You have to have a currency at school,’ Lilly had tried to explain recently, when Mia had told her she felt like a nothing. ‘Something that makes you special.’ It was easy for her older sister to say that. Lilly was both clever and pretty. Whereas until the beginning of year five, when her new friend Tas had appeared at the desk beside her, clutching his red rucksack with the broken zip, Mia could go for whole days without anyone talking to her. As far as currencies went, it didn’t get much better than owning a positive pregnancy test. Surely it would make her more interesting, even to the girls who ignored her.

It was time to get Lilly involved. It felt grown‑up and sisterly to be in a position to share something so intimate, a glimpse of how one day the seven years that separated them might no longer feel like such a chasm. Mia longed for a life of eternal bonds in a world where nothing seemed permanent. She had attended three different schools, had endured five different special-​needs teachers, lost three grandparents and, until she’d met Tas, had never had a friendship that lasted longer than a few weeks.

She spotted the top of Lilly’s head emerging from a cardboard box beside the door into the garden. All she could see of her was the messy blonde bun that was held together with pencils. But even that looked cool.

‘Look what I’ve found!’ Mia tried to sound casual rather than excited. Unlike Tas, Lilly didn’t respond well to her mood surges.

‘Just a minute.’ That was Lilly’s favourite phrase that summer. Especially when it came to Mia. She never said it unkindly. Lilly was always patient with her. But neither did she ever get back to her once Mia had counted to sixty in her head.

They weren’t meant to be in the garage that afternoon. It was full of precariously stacked crates and boxes, packed in haste a couple of weeks earlier so the builders could get started on the damp, which seemed to seep out of the very pores of their new home. But when Lilly had sensed a pre-​lunch row brewing between her parents, uncle and aunt she had dragged Mia away from the barbecue into the hot, stuffy garage.

This was not an act of selflessness to protect Mia from conflict. It was because Lilly knew that if they stayed outside the adults would be more guarded, and the garage was the perfect vantage point to observe what unfolded.

Besides, she needed to unearth a rucksack for a music festival on the last weekend of the holidays. She had bought the ticket without telling her mum because Grace would never agree to her going. The dates clashed with a pre-​term advanced English course at school and her mum was obsessed with Lilly being ‘ahead of the game’ when it came to academic achievement. Until the toilet walls had grown mushrooms, they had been covered with her certificates and awards. Uptight didn’t really cover it.

Lilly knew trouble was brewing because earlier in the week she had overheard her dad describing his brother, Rob, as an ‘A‑grade fuck-​wit’, a phrase he used so rarely that he made it sound as if he was grading an essay by one of his A‑level students. Her aunt Ana, who normally had to try really hard to find Lilly’s parents interesting, had improbably asked to come and see them because she needed some advice.

Lilly felt she had the right to know the reason behind all the tension. She wanted to hear the raw, unfiltered version of what was going on. She wanted to witness Wild Passions and Total Loss of Control. Not least because, over the past couple of months, she had got involved with a boy from school and was going through some emotional extremes of her own. She felt that if they dug deep, underneath the good manners and bad jokes, her parents, uncle and aunt were capable of great drama.

So, she had convinced her little sister they should go and search for Lilly’s collection of gemstones in the storage boxes, promising that if they found them she would give half to Mia for her birthday, including the fool’s gold and agate geode. Lilly knew her sister would find this an irresistible bribe. She liked to consider herself a collector. Her room was filled with bizarre objects: feathers, Allen keys in different sizes, bulldog clips. Her current prize possession was an eel she had found at the end of the garden during the spring floods, who lived in a bucket beside her bed.

‘Look at this ‒ you won’t believe it,’ said Mia, a little more desperately.

‘In a minute, Mimi,’ Lilly replied languidly, without bothering to look up. It was hot and humid in the garage, and when she wasn’t with Cormack, she felt overwhelmed with a languor that only he could dissipate. I’m like an inert gas. I only react with him. She had seen him almost every weekend since June because they both had a Saturday shift at the same punting company in the centre of Cambridge.

Her mum had reluctantly agreed that it would sound good on her university application to prove she could manage a job alongside her school work.

Although Grace hadn’t said so, Lilly knew the extra spending money would come in handy: family finances were obviously tight or why would they have moved to this dump?

But today Grace had insisted she stay at home to have lunch with Rob and Ana. Lilly imagined herself entwined around Cormack in the cool waters at Earith Sluice. That was all that mattered. Everything that used to count – exam results, university entrance, Insta likes, Hayley – had faded into the background. She thought about him all the time. What used to be in that space in her head that he now took up? Or was it some new space he had opened?

Lilly was half-​heartedly examining the contents of a box behind the door, pretending to search for the gemstones, while keeping an ear open for what was going on outside. The box was full of musty-​smelling children’s books. Dr Seuss. Goodnight Moon. Legends of the Fens. Comforting, familiar titles that she had read to Mia years ago when she relished playing mother to her younger sister. She pulled out the Best Friends For Ever diary that she and Hayley had kept from year six to year eight and flicked through the pages. Our favourite colours. Our best swimsuits. A Polaroid of the two of them having their ears pierced. A ticket to Glee Live. She pressed the notebook to her face and inhaled. It smelt like the rest of the house, a thick musty odour that made her feel heavy-​headed.

According to her dad, the reason for the smell was that the dodgy construction company that had sold them the house on the new-​build estate in Black Fen Close last November had ‘forgotten’ to do a proper damp-​proof course. Her mother, in classic Debbie Downer mode, declared that it was because the marshland beneath was reclaiming territory that was rightfully its own. ‘Did you know the North Sea used to come as far as Cambridge?’ she kept telling them.

When they had first moved in and her mum could still joke about the damp because it was confined to one room, Grace had teased Patrick that it was an act of vengeance on him for his Dutch ancestors who had drained the Fens to turn them into farmland.

‘Lil, look!’

‘Have you found the gemstones?’

‘It’s a pregnancy test,’ said Mia, keeping her tone deliberately even. ‘With a clear blue line.’ She was trying to knot her long, curly auburn hair into a bun like Lilly’s, but it was too thick and unruly.

This time there was no ‘Just a minute.’ Lilly looked up straight away, her face a gratifying picture of astonishment. Finally Mia had her total attention. Lilly hastily negotiated a route through the storage crates towards Mia, tripping over her sister’s foot in her eagerness to reach her.

‘Why do you always wear those big black boots?’ she asked impatiently, as she took the pregnancy test from Mia’s hand and held it up to the light for closer inspection.

‘They make me feel strong,’ said Mia, with a shrug.

‘Show me where you found this, Mimi.’

Mia pointed at a large silver tin with llamas embossed on the lid. ‘There’s loads of hippie clothes too,’ she said, holding up a brown suede waistcoat fringed with long tassels. She sniffed it. ‘Smells weird. Sort of sickly.’

Lilly handed back the pregnancy test, removed the lid of the tin and started examining what, in Mia’s opinion, were far less interesting objects, including pieces of torn‑up postcard and a notebook with ‘The Certainties’ handwritten in black felt-​tippen on the front.

‘Why would anyone keep a pregnancy test?’ Mia asked, trying to refocus Lilly’s attention.

‘Because it means something. Because it represents part of how you have become who you are. Because it’s your history.’

‘Weird, huh? I’m going to ask Mum about it,’ declared Mia. She stood up and brushed down her bare legs, sending a flurry of dust into the air. Her denim skirt had shifted around her narrow boyish hips so that the zip was at the side instead of the front. She shunted it back and put the pregnancy test into her pocket.

‘Wait,’ said Lilly, abruptly. ‘You can’t do that.’

‘Why not?’

Lilly frowned so intently that her eyebrows met in the middle. There was a long silence during which Mia tried and failed again to tie her long curly hair into a bun.

‘Because it’s mine.’

‘I found it first.’

‘You don’t understand. It belongs to me.’

For a split second Mia suspected Lilly was winding her up. Then she saw the expression on her face. The last time she had looked so worried was the day she’d got her GCSE results. Even then Mia hadn’t taken her anxiety seriously because everyone except Lilly was certain she would get the highest grades. This, however, was different.

‘You’re pregnant?’ Mia asked. She wasn’t sure what to do. Should she hug Lilly or give her a high five? What did people do on TV? But as she stepped forward Mia accidentally trod on an electronic globe that she had taken out of the box where she’d found the pregnancy test. It started parroting the population rate of different countries around the world: ‘Mexico 132 million. Indonesia 269 million.’ She would have asked Lilly if this was a good example of irony, a grammatical point she was struggling with at school, if she hadn’t been so concerned about what she had just learnt. When Lilly didn’t react, she kicked the globe with her leather boot and it started playing the national anthem.

Mia suddenly felt tearful without understanding why. At first she thought it was the realization that Lilly would always do everything before her and she would never catch up. But it was more than that and worse than that. Mia knew right away that she could never compete for attention with a newborn baby, which made her feel bad about herself. She would be expected to learn to change nappies, prepare bottles, babysit and generally assume responsibilities as an aunt that she didn’t feel ready to take on. And what if Lilly died in childbirth?

‘Past tense. Was pregnant,’ Lilly said. ‘I had an abortion.’

Abortion didn’t feature in David Attenborough or on the school sex‑ed curriculum and at first Mia didn’t understand what Lilly was talking about. It sounded as though she had either hidden the baby somewhere or given it away.

As usual, Mia was playing catch‑ up.

‘What do you mean?’

‘I went to a special clinic and took a special pill so I wouldn’t have the baby.’

This was even more cataclysmic. Now Mia felt regret for the niece she would never know (she had no doubt it would have been a girl) and the ten-​year-​old aunt she would never be. The baby might have grown up to become her closest friend after Tas. They could have gone on holiday together and taken the train to London to go shopping. A period to mourn the loss properly would be required. As Grace often observed about Mia, being contrary was a terrible affliction.

‘Does Cormack know?’

Unlike her parents, Mia knew all about Lilly’s secret boyfriend. A few weeks ago, after a lot of negotiation with Grace, Tas’s mum had arranged for Mia to spend the day at the Travellers’ site where they lived in a caravan. But after lunch, knowing Grace would be at work, the two of them had caught the bus home to release her pet eel, Elvis, for a swim in the pond at the bottom of the garden. Unusually, they were arguing as they carried the bucket across the lawn. The time when the eels would leave the Fens to swim back to the Sargasso Sea was approaching and Tas thought Elvis should be released back into the wild while Mia wanted to keep him through the winter. ‘That’s cruel,’

Tas argued, as they walked down the garden. ‘And unnatural. Like preventing Travellers from travelling.’

Rationally, Mia knew he had a point but emotionally she couldn’t bear to part with her eel. She had felt weary over this dilemma: the pull between doing the right thing and what you wanted to do in your heart gave her an idea of how it might feel to be adult. Because their voices were raised they didn’t hear Lilly and Cormack, who were lying in the long grass close to the pond. Mia tripped over a bare leg, the bucket tipped on its side, and Elvis slithered over Cormack’s bare buttock through the grass towards the pond.

‘What the fuck?’ said Cormack, jumping up to wipe eely slobber from his leg. The water from the bucket stank of old fish, pondweed and the fear of trapped eel.

Lilly hugged her arms around her bare breasts, while Cormack tried to hide his penis with his hands. Mia was too distressed about losing her eel to worry about their nudity. She ran towards the pond, with Tas in hot pursuit. The dust and the long dry grass stuck to Elvis’s slimy skin and slowed him down. Mia caught him just as he slid into the water. His glassy eyes were full of tears as she’d put him back into the bucket and fixed the grille on top.

‘No. You’re the only person who knows,’ Lilly replied.

‘You didn’t tell Hayley?

‘Hayley doesn’t know about me and Cormack yet.’

‘Why not?’

‘We want to keep it low key.’

Mia looked up at her older sister and smiled. Lilly had had sex, got pregnant and had an abortion. The distance between them should have been wider than ever but the fact that Lilly had confided in her alone made it feel as though there was a new closeness in their relationship. Lilly smiled back.

‘Not a word to anyone,’ she said firmly. ‘It’s never to be mentioned again.’

‘I promise,’ said Mia. She paused for a moment. ‘Was it awful?’ She couldn’t help it. Strictly speaking, this might be her last chance to ask any questions.

‘Was what awful?’

‘Getting rid of the baby. Did it hurt? What did they do with the body?’

‘It was the size of a tadpole, Mia. I don’t want to talk about it. Ever. Again.’