Another bus sails past the stop at the bottom of Sandy Hill. Sunny's been sitting there for ten minutes, waiting on the 11A and wondering if she should have used Delilah's phone to warn her parents that she's on her way, but she knows that even if they didn't answer, her plan wouldn't change. She's relieved to find that she still keeps her keys in her purse – and slightly befuddled when she realises she's thinking of herself as two halves: there is the Sunny she is, the one she has lived as her whole life, and there is this other Sunny. The one who has lived this life. And yet she is both, with the memories of original Sunny and the hair of Sunny two point oh.

A fourth bus approaches, the 19, and her heart twinges because if she gets on that bus, she can go back to her flat and root through her life. She can change out of her pyjamas and find her Walkman and maybe pick up on some clues as to who she is now, and her brain has only half kicked into gear when she launches out of the bus stop with her hand raised. This time she remembers the fare hike and drops 70p in the tray, and she settles into the closest seat for the short ride back to Jupiter Court, hoping that Fenfen won't be home.

Not because she doesn't want to see her, but because she is so fucking exhausted and the day is still young, and for the next twenty-four hours at least, she wants to pretend like nothing is wrong. She wants to pack a bag and secure her headphones over her ears and blast Britney all the way home.

She's in luck. There's no sign of Fenfen when Sunny nudges open the door to her flat – thank fuck she hasn't moved in the past year – and she's glad that it smells the same, looks the same. The aroma of Fenfen's perfume and the novels balanced precariously on every surface; the scent of hairspray and the row of fake plants on the coffee table that Fenfen watered for weeks before realising they were plastic.

A heavy sigh wrenches itself from Sunny's chest as she picks her way across the organised chaos she and Fenfen live in, and when she reaches her bedroom – only a few steps from the door, their flat barely big enough for the two of them – it's hard not to throw herself onto her bed and bury herself under the duvet and will sleep upon herself.

This is the sight that should have greeted her this morning: her messy room with three mugs in various stages of growing new cultures; clothes piled so high on a chair that it isn't even recognisable as a chair anymore; a stack of CDs balanced on her dresser, half of the discs in the wrong cases because she has a terrible habit of using whatever's closest and empty when she switches out her music. The stack is higher now. An extra year of music she doesn't remember. Lyrics and melodies she learnt at some point and has now forgotten.

Almost everything is the same. Except for the corkboard above her desk, littered with photos – that's new. There are people in every picture, shots of her and Delilah; her and Ravi; the three of them together; all of them plus Fraser. Her and Vivian. Her with her friends and Vivian. A photobooth reel of miniature pictures: her and Vivian mid-laugh. Mid-kiss. Arms slung around each other; heads pressed together. She looks so happy, and it's so weird to see, so disorientating. Sunny doesn't consider herself to be an unhappy person – she sees herself as mellow, steady, low-key – but she can't recall the last time she felt as happy as she looks in these pictures.

In these photos, she matches her name: bright and sunny, an exuberant beam that shows off her teeth. Sunny never shows her teeth when she smiles. Her canines are longer than her incisors, like a pair of baby fangs; her lower incisors got pushed out of line when her wisdom teeth came in and now the middle two cross over; there's a slight gap between her front teeth that a couple of cruel girls teased her for when she was in secondary school. Sunny doesn't hate her teeth – she's indifferent, really – but she developed a closed-lip smile early in life. It's jarring to see herself so blatantly happy.

Goosebumps prick her arms, fine hairs standing on end. She studies the photos, and she isn't even sure what she's doing when she unpins them from the corkboard and slips them between the pages of the nearest book. The Perks of Being a Wallflower by Stephen Chbosky. She has never heard of the book or the author but the spine is cracked, the pages curling, like she's read it several times already and a new sense of disorientation floors her, knocking her so hard she drops onto the end of her bed with the book clutched in her hand. How many books has she read and now forgotten, lost to that fourteen-month-long gash in time? How much music has she consumed? When a new song plays on the radio, will she know the lyrics already, words she has been singing all year? Or is that knowledge lost too?

"Fuck," she mutters to herself. Sunny finds great comfort in swearing. There's a word for every feeling, a combination of words for every situation, and it's probably for the best that she doesn't drive because she gets creative enough with her internal rage as a passenger on the bus. Slapping the book against her thigh, she stands and digs out a floppy beach bag and starts filling it. The book first. She really should reread it, she thinks. Next is her Britney CD and then her collection of Now That's What I Call Music! albums. The last one she remembers is number 41, with Boyzone and Robbie Williams and The Beautiful South. There are three more in the stack now. She flips over number 44 and scans the back. Robbie's still on there, along with Britney and Steps and several other names she recognises, and for the first time she's grateful that the compilation CDs are so far behind.

She stuffs the lot into her bag and turns to her mountain of clothes that she has deemed clean enough to rewear but can't be bothered to put away again. It's mostly a mix of t-shirts and shorts in various colours; a pastel rainbow of zip-up jumpers and drawstring hoodies from charity shops; a couple of pairs of light wash jeans and her vast collection of patterned leggings and loose joggers. Sunny's style is about maximising comfort and minimising effort – if she could wear elastic leggings and a loose t-shirt every day, she would. The only reason she changes it up is to avoid Fenfen's raised eyebrows. Shedding her pyjamas, she pulls on a pair of soft baby blue shorts and a faded Spice Girls t-shirt and switches her furry boots for ankle socks and scuffed trainers. She doesn't even like the Spice Girls, but it's the softest cotton and it was only 25p in the charity shop.

Armed with plenty of entertainment, a couple of changes of clothes and, most importantly, her Walkman – plus a change of batteries – Sunny scrounges every coin she can find in her room, dug out of pockets and bags and from under her bed. In the kitchen, she grabs a bottle of Sunny D from the fridge and a handful of cereal bars because Delilah's tea is the only thing she's consumed today and now that her initial panic is wearing off, the hunger is kicking in.

Getting on the 11A is like pulling on a pair of comfortable shoes. It brings memories of every time she has climbed aboard with the undertow of excitement about going home, even though home is less than an hour away and she sees her parents at least once a month, if not every other week. She wonders when she last visited her parents in this timeline. Do they know about Vivian? Have they met her? Sunny can't imagine she would hide her girlfriend from her parents – the bonus of being the child of a queer couple – but she doesn't know how serious they are, doesn't know how out Vivian is, doesn't know how public they are.

These are the thoughts she ruminates on as she curls into a window seat with her arm through the handles of her bag, her feet propped up on the wheel arch. Her head rattles against the glass as the engine rumbles. Once she has her music set up and the familiar opening to ...Baby One More Time pipes into her ears, she hugs her Walkman to her chest and closes her eyes.

The album is forty-two minutes long. When the last song comes to an end, Sunny jerks awake and snaps up straight, dazed by a mid-morning bus nap, and she stares out of the window until she gets her bearings and realises her stop is next.

Thank the lord, Britney Spears, she thinks, jamming her thumb against the stop bell and gathering herself and her stuff in time to tumble off at Salter Street. It's a far cry from the bustle of town out here. Fifteen miles out of Black Sands, the scenery shifts from the vast expanse of the ocean to the vast expanse of fields that stretch to the horizon, rolling hills and islands of trees amidst the lush green of spring. It smells like the countryside out here. Cut grass and manure and hay. Hoisting her bag higher on her shoulder, Sunny stretches out her legs and starts on the half mile walk down a quiet, narrow country lane to the ramshackle former farmhouse where she grew up.

There is no sound but the tweeting of the birds, the pretty song of robins and sparrows and the coo of wood pigeons, the rustle of feathers in bushes and the caw of crows in the giant oak tree that marks the halfway point. The bag is heavy and her legs are pathetically tired from rushing around town all morning, so she takes a break at the base of the oak, breathing in the air she knows so well. When she was a kid, she couldn't understand why her parents wanted to be so remote, why they were so happy to be so cut off: she hated that she couldn't walk to her friends' houses, that she had to beg one of her mothers for a lift if she wanted to go anywhere.

Now she can appreciate it. The quiet. The sense of peace that caresses her bare arms and brushes her legs. The purity of sound out here, cut off from the world. Twitters and chirps. The birds and the trees.

If all else fails, Sunny thinks, she can always flee to the countryside and abandon her fears and responsibilities.

Nobody passes her the entire way down the dusty road, which leads nowhere but her house. The only people who use it are her parents and the postman, and occasionally Jasmine from the florist two miles away because Sylvia is a romantic who loves to surprise her wife with flowers. Through the tall trees that surround the property, Sunny spots the cockerel weathervane that sits on the roof above her bedroom, its colours fading since that night over a decade ago that she snuck out onto the tiles and painted the black steel with vibrant acrylics.

The sight makes her pick up her speed until she turns the last bend and the road opens up to a rusted gate that never shuts, the track lined with tall, leafy trees in full bloom as spring unfurls its buds and April flowers start to blossom in the wild but well-loved beds that Martha tends to. Beyond the trees is the house, which looks like something out of a fairytale – all old bricks and vines and scuffed tiles, homey and welcoming and full of life. Even though Martha and Sylvia are the only people there for most of the year, they are by no means alone. Several cats have claimed them – it's always a cat's choice; the human has no say – and a clutch of chickens peck around the yard, enjoying free roam of more than two acres of land.

Sunny's worries slowly melt away. Nothing seems so bad when she's surrounded by the gentle cluck of strutting hens, or the warm body of a cat winding itself around her legs.

"Hey there, Tom," she says to the ginger boy with the fluffiest tail, who is purring madly as he rubs his face against her calf. It makes her think that it can't be long since she was last here. This Sunny is still close to her family. A second cat lopes over to say hello, this one a chunky Bengal called Kiki whose belly swings an inch from the floor. Sunny scoops her up and nuzzles her face in her neck as she says, "Hiya, baby. How's my good girl?"

She stands like that for a while, swaying in the driveway as she cuddles the purring cat and inhales her furry scent, that mix of warm feline and her mother's washing powder. Cats don't care about anything but food and independence and the occasional bit of attention, and it's a relief to Sunny that for this moment she can forget about everything else going on in her life and just hug a cat.

The moment's interrupted when the gravel crunches and Martha comes around the side of the house in a pair of Hunter wellies, her grey-blonde hair pulled up into a messy ponytail. She's holding a trug in one gloved hand and a trowel in the other and with streaks of mud on her shorts, she looks so far from the version of herself that most people meet – the steady-handed surgeon who is confident and cautiously fearless when it comes to slicing out a brain tumour, navigating around the most vital parts of the mind. This is Martha the mother, Martha the gardener, Martha who abandons her tools when she spots her daughter, shucks her dirty gloves and breaks into a beam.

Sunny isn't worried about getting older because her parents are in their sixties and she thinks they're beautiful, grey hair and lines and all – she is secure in her good genes, the knowledge that Shelley women have strong hairlines and good eyesight and sturdy bones and they age like fine wine.

"Sunny! Honey, I didn't realise you were coming so early," she says, crossing the drive in a few long strides to scoop Sunny into a hug once she has let Kiki go. "Gosh, isn't this fun?" She fingers a strand of Sunny's hair. "Is there no end to Delilah's talents?"

"She can do literally anything," Sunny says, and she sinks into her mother's embrace. Martha is a strong hugger who values the importance of human touch. "Hey, Mum."

"Hi, baby." Her mother strokes her hair and rubs her back. "Come in, I'll put the kettle on. Coffee? Tea?"

"Coffee, thanks," Sunny says. She's had her tea fill for the day and now she needs that bitter tang that she douses in milk and cinnamon. The caffeine has no effect, unfortunately – although she needs the energy, coffee has the opposite effect on her upside down brain and tends to make her sleepy. "Where's Mum?"

As a child, she distinguished her parents as Mummy, for Martha, and Mama, for Sylvia. Growing up, both morphed into Mum when she didn't want to sound childish – by the age of ten, a handful of her classmates teased her when she said Mummy (none ever thought to tease her for not having a father; the children didn't care that her mothers were lesbians, only that Sunny sounded babyish). Now, despite using the same word for both parents, context provides the clue.

"She's at work." Martha toes off her wellies and releases her hair from its ponytail. "She's teaching until three and she has office hours until five so she won't be back until six at least, I'd have thought. I was thinking of doing a lasagne for supper, though I suppose we have lunch to contend with before that."

"Sounds good to me." Sunny sinks onto a wooden chair in the cool, slate-floored kitchen. One leg is slightly shorter so she rocks from side to side in a steady tap-clunk-tap rhythm that gives her something to focus on until her mother gives her a withering look, and she tries to sit still. Sunny has never been good at stillness, unless she's reading.

"What is it with you and that chair?" Martha shakes her head but there's a slight smile playing on her lips. "You never could sit still when you were little. Nothing's changed."

Martha rests her hip against the counter as the kettle comes to the boil. She picks out a couple of mugs, her hand automatically going to the one that she knows is her daughter's favourite, the one shaped like a chicken; Sunny doesn't care that the china is chipped, that there's a crack only held together by glaze. Eschewing the conventional measure of a teaspoon, Martha pours coffee straight from the pot into the mugs, a generous sprinkle of instant powder. Even though Sunny is surrounded by that smell forty hours a week, it never gets old. The rich aroma of coffee still signals comfort to her brain, especially when it's her mother making it.

Martha knows to make it sweet, with plenty of milk and a generous shake of cinnamon on top. Her coffee tastes a million times better than anything Sunny ever makes for herself, which she can't understand because she's watched her mother make it so many times; she has copied out every step of the process, but it never comes out the same. No matter what combination of coffee, milk and cinnamon she concocts, it isn't a patch on her mother's creation. Perhaps because Martha makes it with love, the kind of love a mother has for her daughter that Sunny cannot possibly have for herself.

Martha sets the mugs down and pulls up a chair next to Sunny, pushing aside the unopened post and spam mail that sits on the table between them, and she appraises her daughter.

"You're looking good, darling," she says, soft crinkles forming around her eyes when she smiles. "The hair really suits you. Very..."

"Gay?" Sunny offers. Martha laughs.

"Not what I was going for, but yes. Wonderfully gay." She tugs on her own grey hair. "Reckon I could pull it off?"

Sunny purses her lips. "Maybe a blue rinse."

"Tennyson! How dare you equate me with the kind of wrinkled old biddies who get blue rinses. How old do you think I am exactly?"

"I don't think, I know," Sunny teases. "You're sixty-two – you made a big enough deal about your party."

She knows the mistake she's made the moment the words are out of her mouth. Martha's brow creases, just a bit, and Sunny cringes. Her stomach folds in on itself as though it has been dealt a blow.

"You're missing a year," her mother says with a laugh, and she doesn't know how accurate that is, how Sunny misses the year she's lost like a physical thing, how she feels as though it has been carved out of her chest.

"Sixty-three," Sunny murmurs under her breath, running through her list of mental dates and adding a year to each one. Which means Sylvia is sixty-six now; they have been together for forty-three years, and—

I'm twenty-four, she realises with a jolt. She has spent the whole day so far focused on the year she's skipped and only now does she think about her actual age. No longer twenty-three. Soon to be twenty-five. Another year closer to thirty. Still a few years to go, but it unsettles her nonetheless – she has wasted so much of her life worrying about how fast time is slipping away while she is achieving so little, and now she has frittered away fourteen months in the blink of an eye.

"Are you all right, Sun?" Martha asks, the lines between her eyebrows deepening. "You look a little peaky."

Thinking fast on her feet, she says, "It was a bumpy bus ride," and busies her mouth with her coffee. Martha has made it perfectly, of course. Sweet and milky, plenty of cinnamon on top. She holds it against her lips and wonders if it was a bad idea to come here. How is she supposed to make it through a day with her mother without making it blindingly clear that she still thinks it's February 1999? Her cultural references are all out of whack. She's missed an entire season of Friends. She's probably missed the second season of Sex and the City, which she has been waiting so impatiently for.

Not only is she missing the time from her own life, but from everyone else's too. She doesn't know what her mothers are up to, doesn't know where to begin filling in the gaps.

"How's work?" she asks. Gotta start somewhere, she thinks, so it might as well be with small talk.

Martha doesn't answer. Instead, she presses the back of her hand to Sunny's forehead, which is warm from the walk in the spring morning sun but not excessively so.

"What're you doing?"

"Are you sure you're okay, Sunny?"

"I'm fine," she lies. She tries to make light with a strained laugh. "You're the one avoiding the question."

"Because I retired last year."

This is going to be a lot harder than she anticipated. Sunny's hands tighten around her mug, even though the hot ceramic scalds her palms. Another blow to the stomach. This one stirs up nausea, her throat tightening. "Oh, shit. Right. Yeah. Sorry, brain fog."

Martha's expression doesn't ease up. The ache in Sunny's stomach worsens. "We all went to New York to celebrate."

Shit. How typical, the one time Sunny leaves the country, the one time she travels further than fucking Torquay, it's trapped in a timeline that she's not privy to. "Yeah, I remember – sorry, I'm just tired. It's been a busy week at work," she says weakly, before taking the moment to wonder whether she still works.

But then she recalls the woman in the kitchen this morning – Vivian, not a random woman – who asked if she was working today. So she still has a job. Whether it's the same one, she's not sure. She can't imagine leaving Percolatte, but she can't imagine going to New York with her parents either and apparently that's already been and gone. Her eyes are stinging, her mouth dry even as she sips her drink.

Martha moves her hand to cup Sunny's cheek, her thumb under her chin to tilt her head back and look in her eyes. They have the same eyes. The same shade of pale nothing-brown as the shell of a walnut.

"I think you might be coming down with something," she says, and that's big coming from a doctor. Growing up with a medic for a mother, Sunny is used to zero sympathy for any medical issue. She is used to being told to drink water and take paracetamol and have a rest, no matter the ailment she presents, so for her mother to suggest illness? She must be really concerned. That scares her. That's almost as scary as waking up in a new dimension. The last time Martha Shelley acknowledged illness was in the eighties, when she agreed that Sylvia didn't seem quite right and should probably visit A&E – that turned out to be a ruptured appendix that almost claimed her wife's life.

I might have a brain tumour, Sunny thinks. But she can't say that to a neurosurgeon. Because then Martha will reel off the list of symptoms of a brain tumour, and after having lived with her for so many years, Sunny knows the symptoms. She knows that she has at least a couple right now. The constant low-level nausea that she blames on the anxiety of the situation. The gaping hole in her memory. The headache sitting right behind her eyes.

Sunny doesn't argue with her mother. Because that would be a much easier explanation. This is a hallucinatory virus and all she needs is hydration and rest. Yes, it's only eleven o'clock but for all she knows, she worked a long, late shift and she's behind on her sleep, and the thought of bed is so enticing that she just nods.

"Oh, Sunny." Martha sighs and rubs her daughter's shoulder. "I washed your bedding after you were last here so it's clean and fresh. You go and lie down and I'll bring you some water."

"Thank you." When she stands, she hugs her mother again, and Martha holds her so tightly that tears spring to Sunny's eyes. She tries to blink them away but only succeeds in making them fall, and she can't get rid of them before the hug is over and her mother's looking at her face, her thumb brushing her wet cheeks.

"You don't seem like yourself," Martha says, and there, at last, is something Sunny can agree with.

"I don't feel like myself." Another tear falls. Her chin wobbles and her face crumples and she hides behind her hands as her mother hugs her again.

It's the truest thing she's said since she's been here and the flicker of honesty brings respite. It would be easier to tell the truth. But it would complicate things. It wouldn't be worth the temporary relief because her mother wouldn't understand; it's easier for her to think it's a virus or a headache or utter exhaustion. How can she explain that she made a wish so strong that she opened up a crack in the multiverse and fell right through?

So Sunny traipses upstairs to her bedroom and she sinks onto the crisp sheets and pulls the cool duvet over her clothed body, and if her mother does follow with water, she doesn't know about it because she's asleep within half a minute.

*

as the child of two medics, i can confirm that virtually no ailment is taken seriously, and most medical complaints are treated with painkillers, rest, and water