In New York City's garment district, Thana is a young seamstress who works in a small clothing firm. She is friends with Laurie and two other female co-workers, but she lives in a lonely existence in a small apartment in Clinton Gardens. One typical day after work, her boss, Albert, sends his workers home while he tries to please a buyer for his clothing designs. As the four ladies walk down the street, they must march past leering and dirty men who make obscene remarks and come-ons at them. Laurie protests and insults them vehemently, but Thana is silent because she is physically and mentally a mute.
When the three friends leave to enter a subway station for their destination home, Thana goes off on her own. After grocery shopping in a local supermarket, Thana, walking home, is grabbed by a mugger who rapes her in a deserted alley before stealing her purse. Thana stumbles into her apartment unaware that it is being robbed. Held at gunpoint by the burglar, she is raped a second time. But afterwards, Thana grabs an iron and bludgeons the intruder to death.
Momentarily stunned by what she did, Thana drags his dead body to the bathroom and places it in the bathtubThe next day, Thana goes to work as usual. It is clear at this point that she doesn't enjoy her job because Albert is always yelling at all his female employees, or acts patronizingly towards her. When she accidentally burns a shirt that she is ironing when the images remind her of the previous day's event, Albert further yells at her. After work, Thana gets an idea of what to do with the dead man in her apartment. She returns home and spends all night cutting the dead rapist's body into pieces and placing them in plastic garbage bags which she stuffs into her refrigerator and freezer. Over the course of the entire movie, Thana gets rid of the plastic bags of the dead rapist one by one by disposing of them in various locations all over the cityOne day, when Thana gets out of a taxi to dispose of the latest bag, a leering man with a ducktop hairstyle sees her and begins to follow her. When the man retrieves one of her bags and attempts to return it to her without examining the contents of it, Thana runs.
The man runs after her. After a chase through the streets, Thana runs into an alley that has a dead end. When the man catches up to her to "return" the bag, Thana, finally aware that the man intends to attack her, pulls out a gun that she took from the dead rapist and shoots her would-be assailant dead. Thana runs home and throws up in her bathroom in shock and disbelief at what she did. Her nosy and obnoxious landlady sees her running and demands to know what is going on, but Thana refuses to offer a written explanation.
Over the next few days, Thana continues to have trouble concentrating at work, staring off and being negligent. While her landlady continues to annoy and spy on her, her yapping runt of a dog, Phil, continues barking day and night. At work, Albert scolds Thana for not making the best effort. However, he invites her to come to the company's annual Halloween costume party in a few weeks. Thana writes a note to Albert telling him that she'll let him know. Thana also notices newspaper clips reporting findings of an unknown body as well as the mysterious ". 45 caliber killing" of an ex-convict the previous day.
That afternoon, Laurie takes Thana and her two co-workers out for lunch at a local hamburger restaurant. While eating, the four women notice a man and a woman making out nearby in a booth. When the woman leaves, the cocky man tries to flirt with the four women at their table. But Laurie naturally tells him to "fuck off" when he comes on to her and she tells him that she's "not into men". A little later, when Laurie and the other two ladies leave, Thana is beside herself. When Thana leaves the restaurant, the man follows her out and coaxes her to come back to his loft, claiming to be a photographer who would like her to pose for him.
As soon as they enter a building and take an elevator up to what's revealed as a cheap studio, Thana suddenly without warning, pulls out her gun and empties it into the sleazy photographer, killing him. At night, Thana dresses up like a hooker with blood red lipstick, her face pasty white, and goes out with another one of the bags with the rapist's remains in it, leaving a note for the landlady that she's "spending the night with a friend. " After disposing of the bag in a train station locker, Thana ventures out onto the dark streets to look for attackers. Thana sees a pimp beating up a prostitute, and shoots the man dead from across the street before fleeing. She ventures to Central Park where five gang members surround her just as she wanted them to. With quick shots, she guns them all down.
As it begins to rain, Thana leaves the park and is picked up by a limo containing an Arab sheik who pays her $100 for "services". At a red light, Thana kills him and his bodyguard/chauffeur. Thana returns home the next morning, and, further agitated by her landlady's barking dog, gives him some of the rapist's dead body to eat. Thana continues to dispose of parts of the rapist's body, disposing of one bag in the car truck of a man from Georgia state, and other in a bag lady's shopping cart, while she continues working at her job and agrees with Albert's request to attend the costume party this coming Friday.
That night, Thana goes out again looking for more victims. This time dressed in a cloak, partly obscuring her face, she first ventures to Chinatown and attempts to shoot an innocent Chinese man making out with his girlfriend, but the man enters his apartment building, and unknowingly gets away. At a local bar, Thana meets an unhappy man who, seeing that she's a mute, rambles onto her about his bad luck-prone life. Out on the street at a bench overlooking the East River, the man further rambles on about finding his cheating girlfriend first with another man, then with a woman. Thana points her gun at the man's head, but for some reason her gun misfires. The man snatches the gun away from Thana and realizes that she intended to kill him in cold blood, even though he has not made any move onto her.
The man tells Thana that he will save her the effort in which he puts the gun to his head, and pulls the trigger, killing himself. One day, Thana finally reaches the breaking point over Phil's constant barking and takes him out for a walk. She ties the dog to a post at an East River waterfront and points her gun at him. But for some reason, Thana cannot bring herself to shoot the terrified and whimpering small dog, so she leaves him there. That night, Thana goes to the company costume party dressed as a nun with high-heeled boots and red-lipstick where she meets with Albert and the other employees in the midst of partying. Meanwhile, Thana's landlady enters her apartment.
Thinking that Thana might have killed her dog, as it never returned from its walk with her, the landlady looks around for any evidence of foul play. The landlady opens Thana's refrigerator, but by this time all of the trash bags containing the rapist's body parts are gone.... except one which the landlady finds in the freezer. Thinking it may be her pet dog, the landlady opens it and it's the severed head of the dead rapist.
The landlady calls the police where she shows them the head and also tells them where Thana may be. At the costume party, Thana dances with Albert and then retires with him to a nearby office where Albert flirts with her wanting to make out. When he crawls under her nun's habit, he spots the. 45 gun in her corset.
Thana shoots and kills him. Now completely deranged, Thana emerges from the office and begins to shoot at all the men that she sees at the party in a violent, slow-motion sequence. Laurie, failing to stop Thana's rampage by shouting at her, grabs a nearby butcher knife and fatally stabs Thana in the back. Thana screams and whirls around pointing the gun at Laurie, who backs up in terror. But Thana cannot bring herself to shoot a woman. With a mixed look of shock and disappointment in her eyes, Thana stumbles over to Laurie and replies "sister...
. " the only time anyone has ever heard her speak, and falls to the floor dead. Back at Thana's apartment building, her landlady mourns for her missing dog. But Phil is not dead. He runs into the building after apparently freeing himself from the post and scratches on the landlady's front door..