College student Joanne Murphy and her boyfriend, Tim, attend a party on the eve of the winter holiday semester break. While Tim is away on a ski vacation, Joanne will remain on campus to liquidate the furnishings in Dayton Hall, a dormitory that is scheduled for demolition the following month. Assisting Joanne are fellow students Brian Frazier, Craig, and Patti. Another volunteer, Debbie, is unable to participate because of a family obligation, but promises to assist until her parents arrive the next evening. Aware of Tim’s jealousy over her close friendship with Brian, Joanne assures her boyfriend that he has nothing to fear. Tim leaves on his vacation, and Joanne begins the process of selling the contents of Dayton Hall. An unseen observer comes upon Craig and Patti as they engage in a romantic tryst, then follows Debbie as she completes the last of her duties, while her parents wait in their car. Her father grows impatient and enters Dayton Hall, where an unseen assailant clubs him to death on the staircase. Moments later, Debbie finds the body as she descends the stairs, and runs to the car, where her mother has been strangled. When Debbie faints from shock, the killer drags her underneath the car and runs her over. The next day, Patti learns that John Hemmit, the campus eccentric, has not vacated his Dayton Hall room, and she notifies Joanne, who promises to handle the matter. When custodian Bill Edgar complains about the theft of his electric drill, Joanne immediately suspects John and attempts to evict him. However, John refuses to answer the door, so she leaves a note demanding that he leave. While taking out the trash, Joanne encounters Bobby Lee Tremble, who restores and sells discarded items he finds among the campus refuse. He attempts to flirt with Joanne, but is quickly discouraged. Late that night, as Joanne and her coworkers play pool, they notice John watching them through a window and search the building in hopes of evicting him. The search proves fruitless, and Patti, fearing for her own safety, asks to spend the night with Joanne. Elsewhere in the building, Bill prepares for bed when the killer attacks him with the electric drill, boring a hole in the custodian’s head. The next day, Brian and Craig encounter John on campus, and Craig threatens him with physical violence, which Brian considers excessive. That evening, the group prepares a candlelight dinner, but when they discover some of the food missing, John is suspected and they search the building for him. They return to the kitchen to find it vandalized and their dinner ruined, prompting Joanne to call the police. Officer Lewis arrives, and upon hearing John’s description, tells the group that it fits a man who was apprehended moments earlier. Later, Joanne hears footsteps on the roof, followed by an interruption in electrical service. Patti joins Joanne in her room, and they call downstairs to Brian, who is making his way toward them in the dark. However, when he reaches the staircase, the killer shines a flashlight in his eyes and attacks him with a machete. Craig appears moments later, saying that he was in the shower when the lights went out. Joanne waits for Brian in her room while Craig and Patti continue the search for John. Upon entering the kitchen, Craig locates the circuit breakers and restores power while the killer knocks Patti unconscious and places her in a large steamer. Craig returns to Joanne’s room and tells her of Patti’s disappearance, saying that he was struck from behind. He suggests they look for Brian, but instead find John, armed with a machete. Meanwhile, Bobby Lee is unable to sleep and decides to visit the campus, ignoring the pleas of his wife, who suspects him of having an affair. Back at Dayton Hall, John subdues Craig and pursues Joanne as she locks herself inside a room, where she finds Brian’s dismembered body. John begs Joanne to let him in, explaining that he is trying to protect her from the killer. Joanne does not believe him and the pursuit continues until Craig attacks and kills John, aided by Joanne. She embraces Craig, believing the ordeal to be over, until Craig reveals himself to be the killer. After Joanne makes a failed attempt to escape, Craig takes her to the basement and opens several large refrigerators, where the bodies of his victims are stored. He declares his love for her, explaining that the others had to be eliminated so that they could be alone. Joanne pushes him into one of the refrigerators and climbs the nearby ladder that leads to the parking lot. Outside, Bobby Lee hears Joanne’s cries while he peruses the contents of a garbage can, and runs to her rescue. Craig catches up to Joanne and, furious over being rejected, threatens her life. He knocks her unconscious and attacks Bobby Lee as he enters the basement. Bobby Lee overpowers Craig, but when police officers Lewis and Dean arrive, Craig convinces them that his opponent is a murderer. The officers shoot and kill Bobby Lee, then search the building for survivors, while Craig places Joanne’s unconscious body in the incinerator. Outside, Officers Lewis and Dean complain about the smell from the incinerator, but are satisfied that justice has been served.