Petula and Tilda are young artists in New York who make a living as drug dealers. After losing their stash and money while barely escaping police, they are given two days to repay their supplier. The two connect with Daphne, a wealthy, unstable childhood friend who lives alone in a remote rural mansion, in the hopes of finding a safe in her house that is full of money. The girls rekindle an intricate fantasy game they played as children - one in which Tilda assumes the role of a young girl, Daphne as her mother, and Petula a visiting doctor. The game has three rules - everyone must play, no outsiders allowed, and nobody leaves.Daphne makes Petula do increasingly bizarre things as the game progresses, such as hitting Tilda's knee with a hammer and simulating sexual intercourse with Daphne. Tilda suffers from a bad drug trip, interspersed with a flashback of an argument between the three girls during their childhood that lead to Daphne being pushed out of the treehouse and landing on her head, resulting in her current unstable mental state which causes her to believe the game they're playing is real. In the present, Daphne has bound and gagged Petula and Tilda, having fully lost herself to the delusion that she is actually their mother.Daphne is visited by Detective Siegel, who knew all three girls when they were children. Siegel claims that her neighbors have reported hearing screams from her home. Though Daphne's odd behavior makes him suspicious, he leaves after she reminds him that he doesn't have a search warrant. Daphne later gives Petula clues to the location and code of the safe, and promises to free the girls if she can find it. Petula succeeds and the girls escape, but are pursued by Daphne, who runs Petula over with her car before taking them back to her mansion.Daphne cuffs Petula to a chair and locks Tilda in a cage, forcing the latter to watch as she gives Petula a Glasgow smile. The next morning, Daphne tells them that the "game" has concluded and that they are free to leave, but also that she believes she has become pregnant from her faux sexual encounter with Petula. Realizing that this gives them new power over her, Petula restarts the game by convincing Daphne that she needs to be taken in for an emergency caesarean section.Just as the two girls are about to attack an unconscious Daphne with surgical tools, Spiegel enters and holds them at gunpoint, but Daphne wakes up and repeatedly stabs him. Tilda gleefully joins her, while Petula initially watches on in horror, but eventually joins the other two in bludgeoning him to death. They bury his body in Daphne's yard before all three women return to living in the mansion and playing the game, their scars from the injuries inflicted by Daphne having miraculously disappeared. As Petula grows increasingly wary of her surroundings, it is eventually revealed that the entire movie has taken place within Daphne's mansion - every event that occurred up until this point was merely a part of the game, which Tilda is in on as well - and that Petula has tried to escape several times, only to be punished each time by having her arms burned. All three women commit suicide, though this is later revealed to be staged as well when the game starts anew, showing Daphne as an old woman in a withering house, revealing that they have been playing the game for several years.