A NIGHT TO DISMEMBER

The Kent family of Woodmire Lake is thought to be subject to an ancestral curse that causes each of them to be murdered or commit familicide. Bonnie Kent is among the first, found hacked to death with an axe by her sister Susan; after committing the murder, Susan slips in the bathroom and falls on the blade, killing herself. Later, Broderick Kent's wife Lola is found murdered in her bathtub; he initially denies involvement, but soon confesses to the murder before hanging himself. Broderick's niece, Vicki Kent, had been sent to an asylum in the years prior for murdering two neighborhood boys in August 1981.

Six years later, Vicki is released from the asylum, apparently cured of her homicidal tendencies. Her release is against the behest of her brother, Billy, and sister, Mary, both of whom want her recommitted. Upon returning home, Vicki's parents, Adam and Blanche, struggle to help her assimilate. Vicki attempts to rekindle a romance with her ex-boyfriend, Frankie, and is soon plagued by hallucinations. At his home, Frankie and his new girlfriend are killed in the midst of a sexual tryst, the killer decapitating him and burning his head in the fireplace.

With her home life turbulent, Vicki attempts to visit her uncle Sebastian and Aunt Ann; her great aunt Bea is also staying at the home. They turn her away, however, deeming her and her siblings all insane and unsafe to be around. The next morning, when they attempt to leave their house, Sebastian is murdered with a hatchet before Ann is run over with a car. Bea is pursued inside the house and decapitated, and the killer wraps her head in a cloth before storing it in a cupboard. Later while ruminating at the lake, Vicki is chased by a zombie-like male figure who emerges from the water, only later to find it was Billy attempting to scare her.

Later, Vicki attempts to seduce Tim O'Malley, a detective investigating the murders of Sebastian, Ann, and Bea, by performing a striptease. She subsequently hallucinates a sexual encounter between the two. Billy again attempts to torment Vicki, stalking her in a Halloween mask in hopes of driving her back into madness. That night, Mary awakens from a nightmare in which her entire family takes turns stabbing her to death. While Adam and Blanche attempt to console Mary, the home's electricity suddenly shuts off. Adam goes to check the main braker, and is stabbed to death with an ice pick by an unseen assailant. Shortly after, Blanche is brutally murdered in her bed.

Billy finds his parents' bodies and flees the house, only to be clobbered to death with a rock by Mary, who, convinced her family had tried to kill her, murdered him out of fear. Back in the house, she hears a voice beckoning her, and traces it to a hat box, in which she has a vision of Vicki's severed head. Realizing she is in fact responsible for the murders, Mary retreats to the basement where she continues to hear disembodied voices calling her name. She flees outside into the woods, where the voices continue to taunt her.

O'Malley arrives at the house and finds the numerous bodies, along with Vicki, who appears to be in a fugue state, and holding a bloody hatchet. He chases her through the house and the two engage in a physical fight. She strikes him several times with the hatchet, but he manages to overpower her and strangle her to death. In voiceover narration, O'Malley recounts his discovery of diaries from each of the family members, which reveal that Mary committed all the murders Vicki had been accused of, including the murder of the two boys that warranted her psychiatric confinement. Meanwhile, Mary departs Woodmire Lake in a taxi, and murders the cab driver with a hatchet.