Warning: Major spoilers ahead

Six years ago, a young Josephine is pregnant and living in a trailer community with her boyfriend, Kyle Smith, excited for the baby’s arrival. The young couple look over plans for their house and life together, with Josephine saying she can put things on a credit card and pay it off later. Kyle says it’s nice, but doesn’t feel “like them”, but Josephine is dreaming big, imagining a happy life watching their baby sleep. She says even though they’ve both come from a bad place, the baby is a sign of something better for them both.

The next day, Josephine buys a car, looks at apartments for rent, and goes to a baby store, buying clothes and a bassinet for her dream home. But when she gets back to the trailer, she sees Kyle being arrested and taken in by police for trafficking drugs. He says he is sorry and was just trying to get the money they needed to start their life together.

Pregnant and alone, she’s attempts to drag the bassinet box into the trailer, but it breaks, scattering all the pieces on the floor. Grabbing one of the legs, she angrily smashes at her trailer to get her anger out.

Soon after, Josephine is seen in the hospital bed, with a nurse talking to her mother, Irene. Aged just 16 and having lost the baby, the nurse suggests she take her home so she can get better. Josephine overhears Irene say nothing will get better for either of them.

Irene takes Josephine home, but leaves her in the cab, too shell-shocked to go in without her. When she goes to her room, she deletes all the posts from her Instagram and uploads a black square “In Loving Memory of Josephine Murphy” before removing all her artwork from her walls and packing up her room. When she checks on the post, there is only one comment – someone from school, who noted she “didn’t really talk to anyone and may have had mental issues”.

At that point, Irene bursts into the room, furious that she had opened a credit card in her name and maxed it out. Josephine says she didn’t think she had to pay anything back for six months, but Irene informs her it’s so the credit card company can build up interest. Irene furiously calls her crazy and stupid for making things up in her head, causing Josephine to break down in tears, having lost everything as Irene tells her she has to work off the debt.

Josephine is now working at a dive bar alongside her father, Rob Murphy. Closing up for the night, they look over their tips, and she shares that she’s finally paid Irene back everything she owed. She asks to join her dad at a meeting as she doesn’t want to go home.

He reluctantly agrees and the pair head to a swanky office, waiting outside. He jokes that no matter if you’re a bookie or one of the financiers who work in the building, everyone is “playing around with peoples’ money”.

Josephine asks if she can live with him, but he says no, despite knowing how awful Irene is. However, he says that he can get her more work alongside him as a bookie so she can save up and get her own place.

Soon she realises that his line of work is shadier than she thought, with fake IDs hidden under the bar’s cash register, and another situation that sees him leave a house wiping blood off his knuckles. They then drive to a ranch for Easter for Rob to meet up with Colin, where, to her father’s surprise, she asks to work off his debt for him.

The idea shocks Rob, especially as she doesn’t know Colin, and she comments that she doesn’t feel anything anymore, and if she did something for someone she’d maybe feel better. Rob tells her that Irene was right, and she was crazy, which upsets her, so she goes for a walk around the property.

While she’s out there, she meets Milo, who is playing in the garden with his toy frog Mr Chips, and introduces herself to him. He admits that he snuck out of the house, and he’s called his frog Mr Chips because “it tastes like potato chips in his mouth”, and some words taste like food.

This surprises Josephine, who says she gets the same thing and once had a dolphin called Chocolate, and starts to cry. She tells Milo that their brains just work a little differently, but they’re not crazy, they’re special. Milo is then called away by Marissa and he runs off, leaving Mr Chips behind. She decides to take the toy home with her.

That evening, back at home, she looks up Marissa Irvine and scrolls through her Instagram account, fixated on Milo, and realises his birthday is the same as the day she lost her baby. Shortly after, she starts watching him play at school and the park, and starts driving past the Irvines’ lavish house.

Renaming herself “Carrie” and cutting her hair, she starts decorating her bedroom with posters of Canada and pictures of Milo. She stockpiles clothes and food for a five-year-old. When her mum confronts her, saying she doesn’t have a child, Josephine reacts angrily and Irene punches her. She responds by nearly choking her to death. While she lets go, Irene kicks her out, threatening to kill her if she ever comes back.

Shortly after leaving home, “Carrie” has an interview with Jenny, faking an idyllic homelife and past experience. She claims her mom died of breast cancer to prevent further questions. Getting the job to look after Jacob, she befriends Ana – Milo’s nanny – at the school gates so she can get close to Milo and learn things about him.

She then goes to visit Kyle in prison, having not seen him since he’s been incarcerated. She apologises for not visiting him, and he says he understands. Knowing he’s getting out soon, she asks him what he wants to do when he’s free, and that she needs to tell him something important.

Shortly after, at the marathon, Josephine pickpockets Ana’s phone, deliberately leaving it on the side of a food truck so she has to go back to get it. The trick works, and Ana leaves Milo with her briefly to run back for it. But when Kyle arrives and she introduces him to Milo, he realises what she’s trying to do and refuses, storming off into the crowd.

When Ana returns, she goes after him, and he tells her he can’t be part of a kidnapping. Kyle says that she gets too lost in an idea. She insists Milo would be happy with “people who understand him” but he says she’s crazy. Shoving him, Josephine says she can’t live without Milo.

That evening, Kyle and Josephine meet up at Rob’s bar, where she lays out her plan to stage a playdate and send Marissa off to the wrong address to buy them a few hours. Kyle reluctantly agrees because he doesn't want to lose her but is clearly unhappy about it.

Shortly after, she sets her plan into action, kidnapping Milo by taking him out of school while Jacob is distracted elsewhere and saying they’re “going on vacation”.

Taking him to the lakeside rental apartment, she happily plays with Milo, but soon he’s asking to go home. Kyle is left unnerved by it, saying that she knows it’s wrong to have taken him, but she’s insistent he belongs with them. She asks for an update on a passport they were getting made for him. As the forger isn’t answering her messages, she calls her dad for help.

Rob and Kyle don’t get on, but he agrees to help his daughter, seeing as she’s picked up all the tricks she’s used for a disguise and to avoid detection from him. However, when he goes outside to “make a few calls”. Josephine thinks he’s helping, but Kyle’s not so sure. Kyle’s right – Rob is calling Peter with a ransom demand.

As Kyle’s “Marathon Man” photo is circulated by the press, Rob blames him for things going wrong and they need to bolt now. He tells Josephine to take Milo to his motel, while he and Kyle clean up the property to hide any trace of them, or the kid, being there. Once Josephine and Milo are out of the way, Rob shoots Kyle in the back of the head, dumps his body and finishes the clean-up.

The next evening, while Josephine waits at the motel, she spots a gun in one of the drawers and decides to hide it. Milo then asks if it’s his birthday today, and if it is, why isn’t his mom there, which upsets Josephine. She gives him a hug and together they make a blanket fort, with Josephine sharing why birthdays are so special.

In a flashback, we see Josephine while she was still pregnant, learning how to deal with things on her own, as Milo asks what happened to her baby.

Their talk is disrupted by Rob’s arrival. Rob later claims that Kyle must have bolted after seeing his face was in the news and “wasn’t cut out for this kind of thing”. He tells her to go out and get something for Milo’s birthday, and she’ll be fine as she’s in disguise.

When she does, Rob plays hide and seek with Milo, asking him to hide in a cupboard while his friend comes to see him. By the time Josephine gets back with Milo’s birthday cake, he’s dead on the floor, and Milo is nowhere to be found.

Picking up the gun she’d hidden, she roots through her dad’s pockets and takes out a wad of cash and his phone, which had been recording everything.

As Josephine heads to the ocean, she receives a news blast saying that Milo had been returned to his family. At the bottom of the article, among other recent news, is the announcement that Kyle’s body was found in the lake. Realising what her father had done, she takes off her wig and tries to drown herself in the water.

As Josephine’s life flashes before her eyes, we see her holding her baby boy, Noah, having given birth to him successfully. She later leaves the hospital with the baby in a car seat to take him home.

During her drive, distracted and looking at the baby in the back seat, she gets into a car accident, with the car flipping and leaving her for dead.

When she comes around at the hospital, she insists she still heard her baby crying, but the nurse informs her Noah died and she must have been confused. The nurse notes it must have been the other baby in the accident she heard.

Flashing forward to her meeting with Kyle at the prison, she shares with him that she saw Noah, and he was actually alive. She believes the babies must have been switched somehow, which he finds hard to believe.

However, after meeting Milo at the marathon, he comes around and tells her he does agree with her, as the boy looks just like his dad.

We then catch up to present day, with her walking into the Irvines’ house with a gun. She tells them she’s not crazy, and they have her son.