During the Christmas season, a group of sorority sisters residing at Pi Kappa Sig house prepare to celebrate the holidays and begin their winter break. However, their festive mood turns ominous as they receive a series of bizarre and obscene phone calls from an unknown harasser, whom they nickname "The Moaner." Among the residents are Jess, the responsible one with a sensitive secret; Barb, the outspoken and rebellious alcoholic; Phyl, the level-headed friend; and Clare, the innocent and gentle sister. Despite initial dismissals of the calls as a sick joke, the atmosphere becomes tense after Clare goes missing, leaving her father and the housemother, Mrs. Mac, frantically searching for her. The local police, led by Lt. Fuller, are alerted but show skepticism regarding the severity of the situation.

The mood grows increasingly grim when a young local girl is found murdered in the park, heightening anxiety around the campus. The sorority sisters try to continue their holiday preparations, yet unease pervades the house. Jess grapples with a personal dilemma involving her intense boyfriend, Peter, a struggling music student who reacts poorly to Jess's news. As the threatening phone calls escalate in their intensity and frequency, the women realize that the danger may be closer than they could have ever imagined. The holiday season takes a dark turn as the sisters find themselves entwined in a terrifying ordeal that challenges their wits and will to survive amidst the supposed festive cheer.