UNHINGED

Three female college students, Terry, Nancy and Gloria, embark for a music festival in rural Washington. A sudden storm causes Nancy to accidentally crash the car, rendering all three unconscious. Terry awakes to find her and her friends alive, sheltered in a large mansion in the middle of nowhere, owned by the Penroses: the middle-aged Marion, her mother, and their groundskeeper, Norman. Gloria is the only one with serious injuries, so Marion suggests that they spend the night until Gloria is able to leave. Terry and Nancy are invited to dinner with Marion and her embittered and elderly crippled mother. Throughout dinner, Marion's mother rants and raves about her disgust toward men, and how her husband left her for another woman. She also recurrently accuses Marion of bringing men into the home. Later, in a music room, a mysterious man looks menacingly into the windows at the women.

Later that night, Terry finds a human tooth under her bed and later awakes to hear a man breathing heavily upstairs, as though he is masturbating. The next morning, Terry and Nancy take a shower, while someone watches through a peephole in the wall. That morning, Nancy sets off through the woods to reach the town. When she arrives at a rural country road, she is attacked by an unknown figure with a long scythe, who slashes her to death. That evening at dinner, Mrs. Penrose's divulges her views on men and her daughter, while Terry worries about Nancy's absence. That night, Terry once again hears the breathing and goes to investigate. She uncovers the attic, where she finds black and white pictures of two children, and an old tool belt with a dusty gun and machete. She goes back downstairs and sees the man staring in at her through the window, and runs screaming through the house. Marion calms her down and reveals to her that the man is Carl, her developmentally-disabled younger brother. She insists that he is harmless, and Terry goes back to bed.

The next day, Terry goes outside to talk to Norman and asks if he has seen Nancy. Norman reveals that he never spoke with her, and instead tells her a confusing story about two girls disappearing in the woods. At nightfall, Gloria regains her consciousness, and Terry tells her she feels the two need to leave as soon as possible. Terry leaves the room, and an unseen figure attacks Gloria, plunging an axe through her head. Later in the evening, Terry finds Gloria's room empty and asks Marion where she is. Marion suggests she may have gone outside for a breath of fresh air. As she steps outside, Terry is attacked and chased by Carl. She hides in a shed, where she discovers the dead bodies of her friends along with several other dismembered corpses. Carl breaks through the window and tries to grab her, but she manages to escape from the shed and runs back to the house as Carl chases after her.

Hurrying into the attic, Terry takes out the gun and shoots Carl in the head, killing him. Marion rushes upstairs after hearing the noises, and chastises Terry for killing her brother. Terry responds by ordering Marion to look at the bodies in the shed. After a moment of silence, Marion, speaking with in a deep, masculine register, tells her that Carl had nothing to do with what happened in the shed. Terry looks in confusion at Marion, who pulls out a machete. Marion reveals that he is actually Mrs. Penrose's secondary son, and Carl's younger brother, who dresses and presents as a woman. Terry attempts to flee, but Marion knocks her to the ground and maniacally stabs her to death whilst raving about the pressures of pretending to be a woman, and of taking care of his brother and mother. As Terry bleeds to death on the floor, Mrs. Penrose calls for Marion from downstairs, asking if there is a man up there. Marion, covered in blood, responds in his feminine voice: "No, mother."