And why, Alix wonders, has she never heard of Brooke Ripley? Why is her name and the photo of her in the beautiful white dress not synonymous with the summer of 2014? And then Alix realises that in June 2014 she had a sleepless baby and a feisty six-year-old. She was deep down inside the well of early parenthood, so maybe she had seen this story around at the time and totally forgotten about it, or maybe it had been quickly subsumed by something bigger?

She switches screens at the sound of footsteps down the stairs. It’s Josie, still wearing the same outfit that Alix had lent to her on Saturday. It’s now Wednesday. She has her own clothes hanging in her room, cleaned and ready to be worn. Yet she is still wearing Alix’s.

‘I was thinking,’ Alix says. ‘If you’re going to be here for a couple more days, would you like me to go over to yours and pick up some clothes for you?’

She sees a flash of something pass across Josie’s face. ‘No,’ she says, her mouth set firm. ‘No, thank you.’

‘The weather’s turning though – it’s going to be really hot the next couple of days. Pushing thirty. I could pick you up some more of those summer dresses?’

‘Honestly.’ Josie’s mouth softens. ‘Honestly. It’s fine.’

‘Well, let me know if you change your mind.’

‘Yes,’ says Josie. ‘I will.’

‘And what will you do? On Saturday? Where will you go?’

She tries not to stare too hard at Josie as she finds her answer to this question, as she already knows that she will be struggling, already knows that Josie has no plan beyond the end of each day.

‘I suppose I’ll …’ She trails off momentarily. ‘I’m not sure. I mean, how would you feel …?’

Alix feels herself stiffen.

‘I noticed that there’s a fold-out bed. In the study. I mean, I could always sleep there, while your sister’s here? I don’t suppose anyone will be using the study on a Saturday night? And I’d absolutely stay out of your way so that you and your sister can do sister things?’

Alix’s mouth has turned dry. This is it. This is the line that she had put metaphorically inside her relationship with Josie from day one, and each day they have been stepping a little closer and a little closer and right now they are touching it with their outstretched toes and once that line has been breached Alix no longer has any idea how she will regain control of the situation. She knows, with a sickening certainty, that she has to have Josie gone from her house by Saturday afternoon. But she also knows, with a sickening certainty, that Josie is currently controlling her and that making her leave the house before she’s ready to do so would spell the end of the podcast just as it was gearing up towards being something riveting and unmissable. She thinks all of this in the two seconds it takes for her to say, ‘Well, let me ask Nathan. I’m kicking him out of the girls’ space on Saturday night so he might well end up in the study, working.’

She glances quickly at Josie, long enough to observe a slightly menacing back-tip of her head, a cool refinding of her bearings.

‘Well,’ she says, ‘OK. But let me know as soon as you can.’

‘Yes,’ Alix replies warmly. ‘Yes! Of course.’

When Josie mentions that she won’t be going into work that afternoon, Alix invents a reason to leave the house. Everything has been so intense since the moment that Josie and Walter walked into her house on Friday night. Every minute of every day has been overshadowed by the existence of these people and their horrible, messy lives and by the physical presence of Josie and her dog in Alix’s home. Time has lost its form and its meaning. Another weekend is approaching and on the other side of that weekend is the end of the school term and then there will be six long weeks of unstructured time and loose-limbed days and she needs something which feels normal and just for her. She tells Josie she is going to return some library books and then she heads into the park to have her lunch at the café.

The café in Queen’s Park has formed the basis of huge swathes of Alix’s life since she and Nathan moved into the area ten years ago. She sees ghosts and hears echoes of herself at all the different stages of herself; pregnant with Leon, later sitting with a newborn and a five-year-old, with mums from nursery, mums from school, with Nathan and the kids at the weekends. The ice-cream kiosk makes her think of Leon and Eliza with bright blue mouths after eating the bubblegum flavour. The beers in the chilled cabinet make her think of the slightly woozy sensation of daytime drinking on hot summer afternoons. She’s sat at each table at various points, lived different versions of herself in multiple light-refracting fragments. So today she will sit in the café, and she will eat a panini and she will live another fragment of her life and she will try to feel normal, to feel like the Alix of six weeks ago, the Alix who hadn’t met Josie Fair.

She orders her panini, the one she always has, goat’s cheese and ham, and she orders an iced tea, and she sits with her numbered wooden paddle on the table in front of her and waits for her food to arrive and waits to feel normal. But the normal doesn’t come. Maybe normal is over there, she ponders, on the other side of the park somewhere; maybe it’s in the sand pit where she still takes the children sometimes when they’re feeling little. Or maybe it’s on the zipwire in the adventure playground. Or in the petting zoo, which she and Nathan had walked past drunkenly on the night of her forty-fifth birthday, the dark night air still warm on their bare skin.

Her panini arrives and it is the same panini she always has but it doesn’t bring her normal. It feels like Josie has taken Alix’s normal and swallowed it deep down somewhere inside her darkness. Alix thinks of the blood-smeared key under the mattress with the number 6 scrawled on it. She thinks of Josie rooting through her recycling bin while she was out with her family. She thinks of Josie in her home, right now, wearing Alix’s clothes, Alix’s make-up, scattering her hair, her dead skin cells, everywhere she goes. She pictures Josie going into their study, spotting the sofa-bed, going into Alix’s bathroom, taking her foundation. Then she sees Walter having sex with Brooke, Erin with her ear to the wall, Josie pretending it hadn’t happened, getting on with her life.

Alix pushes the panini away and gets to her feet. She needs to get this podcast finished. Get it done, immerse herself in this filth, get to the end of this miserable story, get Josie out of her house and reclaim her life. But first, she needs to walk past Josie’s flat, peer through the window, see if she can get a sense of what Walter might be doing or thinking.

12.30 p.m.

Alix said she’d be gone for an hour. She said they’d do some recording when she returned, if Josie was up for it. An hour is a long time, Josie thinks. A long time to be alone in someone’s house. Alix told Josie to help herself to lunch. ‘Whatever’s in the fridge, just help yourself.’

So Josie peers into the fridge. She sees the rest of the baba whatever it is, the brown stuff that made Fred sick. She shudders. Then she sees a block of cheddar and thinks that a piece of that and a slice of bread and butter will be all she needs. She eats the tiny lunch at the kitchen table, staring blankly into space. Fred snuffles around the kitchen, looking for crumbs. The floor is surprisingly messy. There has been the plastic twist from the top of a loaf of bread on the floor for three days now. Nobody seems to see it. It’s not commensurate with the image that Alix likes to present on Instagram. None of it is, really, not when you look up close. But that doesn’t matter. Josie is not naturally tidy herself, she’s only tidy because Walter likes it that way, and so she feels happy for Alix that she’s allowed to have a plastic bread-bag tag on her floor for three days without it causing an argument.

A moment later she finds herself striding across the kitchen, picking up the tag and putting it in the pocket of her trousers.

She opens and closes the silky-smooth drawers in the kitchen until she gets to the messy one with all the things in it. She leafs through takeaway menus and biros and packets of Handy Andies and bulldog clips and books of postage stamps and bottle stoppers and rubber bands. Everything has been thrown in, there is no order to any of it. Her fingers feel the sheen of a photograph and she pulls out a column of passport shots. They’re of Leon looking sombre and serious, the pale-blue collar of his school shirt just visible. She slides it into her pocket too.

She thinks of her underwear drawer, at home, of the trophies and trinkets tucked away behind her pants. Not just Alix’s. The others too. She feels an itch to go home, just for a moment, to tuck the child’s drawing and the bread tag and the photos of Leon into the drawer. She could do that, she’s sure. She’d be in and out in seconds. Nobody would see her. She’ll go tomorrow, she decides, after work.

And then she pulls out a shiny black business card with Nathan’s details on it. The name of his company – ‘Condor and Bright, Commercial Property Consultants, EC1’ – and his mobile phone number beneath his office number is printed on it. She puts it in her pocket.

Hi! I’m Your Birthday Twin!