Donna Keppel returns home from the cinema to find her former teacher Richard Fenton waiting for her, having already murdered her father, mother and brother. Donna hides under the bed and Fenton is arrested. Some years later, Donna is living with her aunt and uncle and approaching her senior prom. On Prom Night, Detective Winn, who came to Donna's rescue that fateful night, learns that Fenton has escaped. Donna attends the prom at a nearby hotel, with her friends Lisa and Claire, their boyfriends Ronnie and Michael, and her own boyfriend Bobby. Fenton arrives in disguise, gets a room on Donna's floor and steals the master key. Claire has an arguement with Michael, so Donna takes her upstairs to calm her down. After Donna returns downstairs, Fenton appears and murders Claire. Michael comes to find her and is killed when he opens the closet, which is were Fenton is hiding.
Winn arrives at the hotel to warn the staff of Fenton's potential presence, while Fenton changes his costume. Lisa and Ronnie bump into him in the elevator and when Lisa realises who he was, she runs to warn Donna. Fenton, however, chases her to the boiling room and kills her. Fenton then runs into Donna and he chases her while Winn has the hotel evacuated. He eventually finds Donna and they escape together. Fenton, meanwhile, murders a hotel employee and slips away in his clothes.
As the commotion dies down, Donna and Bobby go home but Winn finds his partner's body in the squad car and realises Fenton has escaped. He races back to Donna's house, when Fenton slits Bobby's throat and then chases her throughout the house. During a struggle, Donna stabs Fenton with a kitchen knife as Winn arrives. Donna cries over Bobby's corpse as Fenton suddenly awakes and lunges for her. Winn then finally shoots and kills Fenton.
- Donna's father - Stabbed to death by Fenton.
- Donna's brother - Stabbed to death by Fenton.
- Donna's mother - Choked and stabbed to death by Fenton.
- Housemaster - Throat slashed by Fenton.
- Claire - Stabbed in the chest by Fenton.
- Michael - Pinned to the floor and stabbed in the chest by Fenton.
- Lisa - Throat slashed by Fenton.
- Hotel employee - Stabbed by Fenton.
- Detective Nash - Stabbed to death in patrol car.
- Bobby - Throat slashed by Fenton.
- Richard Fenton - Stabbed in the chest by Donna with a kitchen knife and then shot several times by Winn.