Plot summary

The film begins at Heathrow Airport, where Lena, a polish immigrant (Olga Fedori) is working her shift as a cleaner. While there, her colleague Birdie (Ainsley Howard) helps her to clean the toilets. Lena talks about her family and living alone in Hounslow. Lena pulls out a mirror that her grandmother left her, and Birdie takes a shine to it. They get some sandwiches, and Birdie introduces Lena to her adopted brother Elbie (Toby Alexander). Lena tells Birdie that she doesn't get on with her family. Birdie tells Lena that her family care for her, and that they work at the airport too.Lena tries to get Elbie to talk to her, but he doesn't respond. Later, Birdie tells Lena about someone they know who has a dirty sexual fetish, before stealing an MP3 player from the office. She tells Lena that people shouldn't leave things lying around if they don't want them stolen. Lena sees some scars on Birdie, and she tells her that she used to have behavioural problems but she is better now.Afterwards, Lena misses her bus home, and Birdie invites her to stay at her house, near the end of the runway. They climb through a hole in the fence, and enter the house through the back door. Lena discusses how difficult it is to keep in touch with her family.Birdie disappears up the stairs, and Lena decides to look around the house for a while, only for Dad (Perry Benson) to knock her out, and inject her with something. She wakes up in a dark room after hearing tortured screaming. She gets mad, and Dad arrives with Mum (Dido Miles), who tells Lena that when she gets mad, Dad gets excited, and they need to calm him down. Dad spits on the floor, and then leaves the room. Mum tells Lena that as long as she is with her, Dad won't hurt her.Lena is unable to speak, and Mum tells her not to try to talk, because she has had a little jab. She gives Lena another injection, and Lena falls asleep. She wakes up later, tied to a frame. Mum tells her that she wanted another girl to come and live there. Mum then pierces Lena's skin with some metal and carves some marks into her back.Mum takes Lena in to see Dad, who is masturbating. When he finishes, he tells Lena that in his house, she abides by his rules. He then grabs her by the throat, before sending her to bed, The next morning, Birdie cleans Lena's scars and she shows her the scars on Elbie's back, which she compares to crazy paving.At breakfast, the family are watching pornography, as Birdie plays with Lena's mirror. She then puts the MP3 player into a pot, and tells Mum that she couldn't get any more stuff because she was doing Lena's work. Lena tries to escape, but Dad grabs her and tells Mum to control her children. Elbie drags her on to a chair, and Mum tells her not to go anywhere.Birdie takes Lena through her chores, and tells her that Elbie has nothing going on in his head or in his pants. Mum arrives and tells Lena that she is doing a good job. In her room, Lena attempts to escape, but hears Dad watching her through the keyhole.At breakfast the next day, Lena sees that Birdie has been hiding money from the family and takes it from her pocket. Dad accuses Birdie of lying to the family and shouts at her. Mum sends her to her room, where she cries before making a mess of what Lena has tidied up. When Elbie arrives, Birdie tells him that Lena is his replacement, and he shoves her to the ground. She compares him to the "spastic thing" upstairs.Later, Lena massages Mum's feet until she falls asleep before doing the same to Dad, who asks her to kiss his foot and make him happy. He shouts at her and throws her to the floor. The next morning, Lena greets Mum with a hug and tells her that her voice is back. Birdie tries to convince Mum that Lena is hiding things from her, but Mum shouts at her instead. Mum attempts to give Lena a top up of the voice paralysing drug, and Lena tells her that she won't scream because of Dad. Mum tells her it is much nicer when she plays along, before cutting her leg open.Lena does her chores and finds a mobile phone, which she hides in her knickers. Birdie phones the phone, and Mum finds it, and tells Lena that she is very disappointed in her, before getting Elbie to hold her down while she gives her a stronger dose of the drugs.Later, Lena is washing clothes, when she hears a man outside. She tries to get his attention by calling for help and when that doesn't work, she throws a human tooth out of the window. Dad sees it and blames the roof. He rushes upstairs and drags Lena into his torture room, before putting her inside a suitcase and making Elbie hit it with a hammer.The man enters the house, where Mum is waiting, and suffocates him with some bubble wrap. After the man has been chopped up, Dad tells Lena he warned her of what would happen if she broke the rules before making her kiss the man's decapitated head, then choking her again.The next day, Mum tells Dad she has a surprise with the man's parts, and makes them into sausages, as Birdie tells her about some new girls at work on dodgy visas.After spending the night tied to the radiator, Lena breaks into the torture room, and finds a staircase up to the attic, where she sees a mentally ill girl in bed (the spastic that Birdie was referring to). The girl wakes up and has a fit, but Lena calms her down, before finding a man in the torture chamber, and calming him down too, before stealing a weapon.The next morning, Birdie enters Lena's room and tells her it's Christmas. She goes downstairs to find the man crucified on the wall, and "the spastic" in her chair. Dad pours wine down Lena's throat before spitting in her face. She bites him, causing him to hit her on the head. They open their presents next; Birdie has been given some knives, and Elbie has been given some porn.Dad tells Lena that he knows she has been visiting "the spastic", and she is like that because the cord was wrapped around her neck when she was born and she is his real daughter. He calls Lena a pet, and tells her a pet isn't for life, just for Christmas. Mum can't bear to look at "the spastic" and tells Dad she shouldn't even be there in the first place. Mum gives Lena a dress for Christmas and they get her to try it on.Dad arrives in Lena's room wearing a dress, and unties her, causing her to stab him with the weapon she stole from the torture chamber. She makes her way downstairs, followed by Dad, who collapses, causing Mum and Birdie to rush to help him. She stabs Mum, then Birdie attacks her, but Lena slams her into a wall and takes Dad's knife, stabbing her in the stomach.She opens the back door, but Birdie attacks her again, so she hits her over the head with the iron and rushes outside. She climbs over the back gate, but falls and twists her ankle. Mum and Dad rush out, bloodied and battered, chasing her. She fights them off, and stabs them both repeatedly. Meanwhile, Elbie sets "the spastic" free of her restraints, before strangling her. He then walks out of the front door. The final shot is of Lena screaming in the field.