Two couples—Tony [Greg Rhodes] and Helen [Claudia Franjul], and Rod [Mark Irish] and Susan [Liz Hitchler]—are traveling by car through upstate New York toward a lake, with their friends Peter [Jerry Kernion] and Anne [Kathleen Patane] following behind on a motorcycle. En route, the group pick up Jack [Clark Tufts], a hitchhiker who claims to be familiar with the area, but is in reality an escaped convict. As night falls and they fail to arrive at the lake, Rod decides to pull off onto a side road and camp overnight. At the end of the winding road, they come across an abandoned house and decide to spend the night there. In the yard, they find a burned, damaged car oddly parked atop a stone monument. Inside is a photo of a beautiful young woman, along with articles of clothing; they determine it to be a bizarre shrine of some sort.
Helen [Claudia Franjul] finds the home profoundly frightening, and refuses to spend the night there; she leaves, telling the others she will go on to the nearest town, but is murdered in the woods by an unseen assailant. The group manage to break into the home, and begin exploring. In the basement, they find a number of sealed coffins, and more photos of the unknown woman pasted on the walls. Further evidence suggests someone has recently inhabited the home. They are further disturbed when they come across a closet full of mementos, including what appears to be a human scalp.
The group fall asleep in a parlor after starting a fire in the fireplace, the heat of which begins to cause a plaster wall to crack. Tony, unable to sleep, continues to explore the upstairs of the house. In a drawer, he comes across a photo album containing pictures of what appears to be nude corpses. Tony eventually falls asleep on a bed, where he dreams of having sex with the woman in the photographs. Tony returns to the basement, and finds one of the coffins, labeled "Amanda," open. Jack confronts Tony in the basement, accusing him of stealing items from the house. Tony goes outside and sits in the car atop the stone monument to smoke a cigarette.
Rod and Susan awake and go upstairs to have sex. When Rod goes outside to retrieve condoms, he is attacked and killed. Moments later, Susan sees a woman wearing an expressionless white mask staring at her through the window. Susan subsequently has her throat slashed when she goes to find Rod. Meanwhile, Tony finds Helen's bloody corpse concealed inside the wrecked car. His screams awaken Peter and Anne, who find him crying over Helen's corpse outside. In the adjacent barn, the three find numerous vandalized motorcycles buried in hay, including Peter and Anne's. When Tony attempts to start his car, he finds it has been tainted with. Peter and Anne flee to the nearest road to flag down help, while Tony searches the house for Rod and Susan. He is confronted by a dying Jack in the stairwell, his throat slashed. Tony flees into the basement, where he is stabbed to death by the assailant.
Peter and Anne manage to flag down Alfred [Richard Rohr], a aristocratic middle-aged man driving by. When Anne notices yet another photo of the mysterious woman on the dashboard, Alfred stabs Peter in the throat with a hunting knife. Anne flees into the woods with Alfred in pursuit, and returns to the mansion. She discovers the bodies of Tony, Rod, and Susan. Upstairs, she is confronted by the killer—Amanda, the wife of Alfred and the woman in the photos, who was horribly disfigured in a car accident caused by a reckless biker gang. Driven by vengeance, she and Alfred trap and murder young people passing through the area.
Anne unsuccessfully attempts to reason with the psychotic Amanda, and is cornered by her and Alfred downstairs. In a struggle, the cracking plaster wall gives way, revealing a cache of corpses. Before Alfred can stab Anne, police officers who have arrived at the mansion to arrest Jack, who had been spotted in the region, shoot Alfred dead. A distraught Anne and raving Amanda are escorted away from the house in separate police cars.
