Twenty-one year-old Chris McCormick (Margaux Hemingway
) is a top model for a company selling lipstick. McCormick has responsibility for her 14 year-old sister Kathy (Mariel Hemingway
) as their parents were killed in a car crash. They share an apartment and Kathy attends a private, Catholic school.
Kathy invites her handsome, young music teacher, Gordon Stuart (Chris Sarandon
) to come to one of Chris's photo shoots along the ocean because she wants her older sister to hear his somewhat avant garde musical compositions. The shoot runs long, so Chris does not have a chance to hear it, but arrangements are made for him to stop by her apartment the next day to play it for her.
The next day, Stuart arrives at the apartment, but Chris has forgotten the appointment and this causes her to greet him fresh out of the shower dressed in nothing but a robe. Stuart obviously hopes that if she likes his music she might be able to use some of her musical connections to help him. While he is playing a selection from his tape recorder (the composition uses a lot of environmental sounds with electronic synthesizers) Chris is interrupted with a phone call from her boyfriend Steve Edison (Perry King
) and retreats to her bedroom.
The interruption and Chris's apparent apathy toward his music enrages Stuart and he enters her bedroom smashing things and hitting her. He then throws her naked across her four poster bed and secures her spread-eagle on her stomach with silk scarves to the posts and sodomizes her.
Toward the end of the rape Chris has stopped struggling so when little sister Kathy arrives home from school she enters the apartment and hears nothing amiss. She walks into Chris's bedroom via a connecting balcony and sees the scene, but does not realize that Chris is being forced against her will, so she leaves quietly, shutting the patio door behind her.
Chris hears the patio door shut and realizes that Kathy must be home and begs Stuart to release her. After half-jokingly suggesting they make it "threesome," he does, noting that Kathy must think "her sister just made it with her favorite teacher." Stuart leaves and a crying Chris stumbles to Kathy who finally realizes that something is wrong.
The police arrive and gather evidence while Chris talks to a rape-crisis counselor. Later that night the police pick up Stuart and take him to jail.
A few days later Chris, Edison and Chris's priest/brother, Martin (John Bennett Perry
) meet with district attorney Carla Bondi (Anne Bancroft
). Bondi warns Chris that getting a conviction under these circumstances (she invited him to her apartment) will not be easy. Edison also has his doubts about pressing charges as he fears it may damage Chris's career. Chris makes it clear that she want to go ahead, however.
Stuart's attorney Nathan Cartright (Robin Gammell
) does everything he can to raise doubt in the jury's mind about whether the encounter was consentual even bringing in Chris's sexy pictures from the photo shoot in an attempt to besmirch her reputation. However, in the end it is Chris's own sister's testimony that gets Stuart off the hook: despite Kathy's protests that she believes her sister's story, it is clear that the afternoon of the attack Kathy's failure to call the police after seeing them together in the bedroom is a clear indication that she did not think at the time that her sister was being raped. The jury acquits Stuart.
Chris tries to go back to work, but it is clear that she cannot focus her attention on her modeling and the lipstick company decides to suspend her contract. Kathy switches schools as it looks like Stuart may get his old job back.
Kathy is watching her older sister at one final shoot being done at a partly completed mall complex and gets bored. She starts exploring the empty mall and stumbles across Stuart and some of her former classmates preparing a dance performance to his music. When the classmates leave, Stuart sees her and invites her to help him with the final mixing of his composition. She approaches and lets him place a contact microphone on her chest to record her heartbeat to add to the music. We hear her heartbeat suddenly speed up as Kathy realizes that Stuart is making sexual advances toward her. She runs and he chases her through the empty mall until he catches her in a sub-basement tunnel. There we see him start to tear her clothes off and the scene ends.
Kathy stumbles back to the part of the mall where the photo shoot is going on. She crying and her clothes are torn. Chris asks what happened. At first Kathy tells her nothing, but then admits she ran into Stuart and he attacked her.
Chris races to the window and sees Stuart leaving the building. She runs down to her truck and gets a rifle she has in the back and shoots Stuart as he is driving from the parking lot. He crashes his car, then climbs out, but is shot again and again by Chris, including a shot to his genitals. She continues to try and pump bullets into his dead body even after he has stopped moving and the gun is empty. We see the police arrest Chris who is in a state of shock. As the camera pulls away from the scene we hear Bondi, who has apparently left the D.A's office to defend Chris, tell the jury that justice can only be served if they acquit Chris of Stuart's murder.