Walking home from work one night, Thana, a mute seamstress in New York City's Garment District, is raped at gunpoint in an alley by a mysterious, masked attacker. She survives and makes her way back to her apartment, where she encounters a burglar and is raped a second time. Thana bludgeons this second assailant to death with an iron. She then keeps his .45 caliber M1911A1 pistol, dismembers the burglar's body, puts the pieces into plastic garbage bags and gradually disposes of them in various locations throughout the city. She begins to have frequent nightmares and hallucinations of the first assailant stalking her, and her mental stability begins to dim.
Thana is noticed by a man while she is disposing of one of the bagged body parts; retrieving the bag, he chases and frightens her. Fearing another sexual assault, she fatally shoots him. This event furthers her impulse for vengeance. Gradually, Thana transforms her appearance to become a more and more seductive bait, and sets out to kill any man who annoys her. Near the end of the film, she dons a nun's habit and red lipstick to attend a Halloween party with her boss and co-workers. Her boss tries to take advantage of her and is killed; Thana then begins a shooting spree and targets all the men present. Finally she is stabbed by a female colleague.
