Twenty-one-year-old Chris McCormick (Margaux Hemingway), a prominent model for a lipstick brand, is tasked with caring for her younger sister, Kathy (Mariel Hemingway), after their parents tragically died in a car accident. Together, they live in a shared apartment while Kathy attends a private Catholic school.
Kathy, eager for her sister to experience the avant-garde musical compositions of her charming young music teacher, Gordon Stuart (Chris Sarandon), invites him to one of Chris's photoshoots by the ocean. However, when the shoot runs longer than expected, Chris misses the opportunity to hear Stuart's music. They arrange for him to come to their apartment the following day.
The next day, as Gordon arrives, a forgetful Chris greets him right out of the shower, only clad in a robe. Gordon, hopeful that Chris may use her industry connections to foster his musical career, begins playing his compositions on a tape recorder, which intertwine environmental sounds with electronic synthesizers. Unfortunately, Chris is interrupted by a phone call from her boyfriend, Steve Edison (Perry King), prompting her to retreat to her bedroom.
This disturbance infuriates Gordon, leading him to violently confront Chris in her bedroom, where he proceeds to assault her in a grotesque act of aggression. Amidst the chaos, young Kathy unexpectedly returns home from school. Unaware of the horror unfolding, she quietly enters Chris's room from the connecting balcony, only to inadvertently leave after witnessing a scene that she misinterprets.
Upon realizing Kathy's presence, Chris pleads with Gordon to let her go. He coldly relishes the notion that Kathy may believe her sister engaged willingly with her favorite teacher. Once freed, a devastated Chris seeks her sister, who, after gaining comprehension of the situation, is horrified.
As the police gather evidence, Chris receives support from a rape-crisis counselor, while Gordon is arrested later that night. A few days later, Chris, Edison, and their priest/brother Martin (John Bennett Perry) consult with district attorney Carla Bondi (Anne Bancroft), who delivers a sobering warning: securing a conviction in such circumstances, especially since she initially invited him over, may prove to be arduous. Despite Edison’s reservations about the potential repercussions on her burgeoning career, Chris is resolute in pursuing justice.
In the courtroom, Gordon's attorney, Nathan Cartright (played by Robin Gammell), attempts to discredit Chris, even showcasing her provocative modeling photos as evidence of her questionable character. Ultimately, it is Kathy’s testimony that leads to Gordon’s acquittal, as the jury interprets her failure to act during the encounter as a sign of consent.
Determined to return to her modeling career, Chris finds her focus increasingly eludes her, resulting in the suspension of her contract. Meanwhile, Kathy changes schools, fearing the implications of Gordon's potential reinstatement.
During a crucial photo shoot in an incomplete mall complex, Kathy, feeling disinterested, explores the space and happens upon Gordon, alongside her former classmates, preparing for a dance performance. When her classmates leave, Gordon calls her over to assist him with mixing his composition. As he places a contact microphone on her chest, recording her heartbeat, she suddenly realizes the precarious situation she is in. In a panic, she attempts to flee, but Gordon pursues her, ultimately trapping her in a deserted sub-basement tunnel.
Desperate, Kathy manages to escape back to the photo shoot, visibly distressed and with her clothing in tatters. Initially reluctant to speak, she eventually confides in Chris about Gordon's attack. Enraged and filled with protective instinct, Chris rushes to retrieve a rifle from her truck and confronts Gordon as he attempts to leave. In a moment fueled by rage and despair, she opens fire, hitting him multiple times, including a fatal shot to his genitals. Even after he falls, Chris continues to fire until the weapon is emptied, trapped in a state of shock over the horrific chain of events.
As the police arrive and apprehend Chris, a solemn reflection unfolds. The camera pulls back to reveal Carla Bondi, who has stepped away from the district attorney's office to take up Chris's defense, addressing the jury in her murder trial, emphasizing that true justice hinges on their decision to acquit her of the charges.
