In 2007, David Moran, a Wall Street player, witnesses a manhit and run by a car. He responds to the situation and tries to resuscitate the victim. That evening, he reflects on his past in the summer of 1958, when he meets his first teenage crush, Meg Loughlin. Meg and her disabled sister Susan have lost their parents in a car accident and are now living with their aunt, Ruth Chandler, and her sons, Willie, Ralphie, and Donny. Ruth freely allows her sons and their neighborhood friends to her house, where she entertains them and offers them beer and cigarettes. Meanwhile, Ruth starves Meg, accuses her of being a whore and subjects her to misogynistic lectures, whilst her children listen. She even beats Susan after Meg hits Ralphie when he inappropriately touches her. Meg reports the abuse to Officer Jennings. As punishment, Ruth and her sons bind Meg in the basement and torment her, strip her, and then leave her overnight, hanging by the arms from the rafters. She eventually becomes dehydrated and is unable to even eat the dry toast that Ruth feeds her. Ruth again beats Susan as punishment for Meg. With Ruth's approval, the neighborhood children visit the Chandler residence to tie, beat, burn and cut Meg for fun. Ruth cauterizes the wounds Meg receives with cigarettes. David tries to tell his parents but is unable to do so. Officer Jennings checks in once more, answering a call about Meg being used as a "punching bag". Before answering the door, Ruth threatens to kill Meg and David if they make a noise in the basement. While Ruth and her sons are upstairs, David loosens Meg's bindings and tells her to escape that night. She is unsuccessful. David returns to the Chandler house and is guided to the basement, where Meg is being raped as punishment for trying to escape. Ralphie suggests to Ruth that she should “cut” Meg so that she'll be known as a whore. Ruth agrees and carves the words "I FUCK, FUCK ME" on Meg's abdomen with a heated bobby pin. She taunts Meg about how no man will want her now. Ruth then decides to perform a clitorectomy. David attempts to flee, but is caught and tied up. Ruth mutilates Meg's vagina with a blowtorch. The next morning, David awakes still on the basement floor. He frees himself from his bindings and finds Susan sitting with an unconscious Meg. Susan tells David that Meg did not escape because she was caught trying to take Susan with her instead of waiting to come back for her. She blames herself for telling Meg about Ruth molesting her. David plans their escape, and lights a fire in the basement. As Ruth enters, David bludgeons her to death with Susan's crutches. Willie and Donnie come down to the basement, and Willie attacks David with a knife. Officer Jennings intervenes and arrests the Chandler boys. The police take Susan from the basement and leave Meg with David. She dies after thanking David. Back in 2007, the adult David reflects on how his past still haunts him to his present day, though as Meg taught him, "It's what you do last that counts."
The film had a polarizing effect on film critics. On Rotten Tomatoes, it currently holds a 67% "Fresh" rating. In contrast, Metacritic assigns it a 29. Stephen King said about the film, "The first authentically shocking American film I've seen since over 20 years ago. If you are easily disturbed, you should not watch this movie. If, on the other hand, you are prepared for a long look into hell, suburban style, The Girl Next Door will not disappoint. This is the dark-side-of-the-moon version of Stand by Me."
