The Polish-born Trelkovsky, a file clerk and naturalized French citizen, inquires about a room to rent at a shabby Parisian apartment building. The abrasive concierge is reluctant to give him information until he gives her money. She shows him a furnished apartment and reveals that the previous tenant, Simone Choule, was hospitalized after a suicide attempt in which she jumped from her window. Trelkovsky convinces the landlord, Monsieur Zy, to rent to him, after agreeing not to be loud or bring women to the apartment. Trelkovsky visits Simone in the hospital and finds her covered with bandages, but can see in her gaping mouth that she has a missing tooth. At Simone’s bedside, Trelkovsky meets her distraught friend, Stella. When the patient lets out an anguished scream, Stella and Trelkovsky leave together and, over a drink, discuss Simone, who Trelkovsky pretends to know. They go to a movie and fondle each other in the dark, but stop when they see a man glaring at them. From his office, Trelkovsky calls the hospital to inquire about Simone and learns she passed away. When he returns to the apartment, Trelkovsky unpacks his belongings and rearranges furniture. In the closet he finds a dress belonging to Simone. Looking out his window, he sees a hole in a glass awning through which Simone fell and discovers he can see across the court into the apartment building’s shared bathroom, which another tenant is now using. At a local coffee shop, the owner tells Trelkovsky he is sitting in Simone’s usual spot and gives him chocolate, instead of coffee, which he says Simone liked to drink. When Trelkovsky asks for a particular brand of cigarettes, the owner says he is out of them and offers the brand Simone smoked, but Trelkovsky declines them. Afterwards, Trelkovsky attends Simone’s funeral service and again sees Stella. During the sermon, he hallucinates that the priest is speaking directly to him, taunting him. Later that evening, Scope, Simon and other friends from work come to Trelkovsky’s apartment for an impromptu party and their raucous behavior elicits complaints from an upstairs neighbor. The next day, Trelkovsky is taking out the garbage when he encounters Zy, who chides him about the noise. As Trelkovsky continues down the stairs, pieces of garbage spill out of his bags, but when he attempts to clean it on his return trip, he finds no fallen trash. In his apartment one evening, Trelkovsky sees someone in the bathroom, standing still and staring blankly. He also notices a small hole in his apartment wall, in which he finds a tooth. Fellow tenants, Madame Gaderian and her young daughter, knock on Trelkovsky’s door and ask if he complained about them for making noise. When Trelkovsky says he has not, Gaderian accuses another tenant, one she calls an “evil” older woman, for making the noise and says the woman is making things difficult for her. Trelkovsky later tells Scope and Simon about the complaining neighbors, and when he visits Scope’s apartment, Trelkovsky is shocked when his friend plays a record so loudly as to intentionally provoke his neighbors into complaining. When a neighbor comes to the door, Scope rudely refuses to turn down the music and tells Trelkovsky, “That’s how you deal with them.” One evening, Trelkovsky opens his door after hearing a knock, but no one is there. Through the window, he again sees someone standing perfectly still and expressionless in the bathroom. When Badar, a friend of Simone’s, arrives at his door, Trelkovsky invites him in and tells him of her death. Because the devastated Badar mourns loudly about the news, Trelkovsky, fearing neighbors’ complaints, takes him out. They drink until early morning and Badar confesses that he had an unexpressed love for Simone. On his way home, Trelkovsky stops at the coffee shop and again is served hot chocolate. This time when he is offered her brand of cigarettes, he buys them. Returning home, Trelkovsky finds that his apartment has been vandalized and is again confronted by Zy, who accuses him of making too much noise the previous night. When Trelkovsky explains he was robbed, Zy takes offense, asserting that he has a respectable house with decent tenants, and insists that Trelkovsky not report the robbery to the police. At a bar in the evening, Trelkovsky asks for the brand of cigarettes Simone smoked. He also encounters Stella, who is there with friends, and learns from them that Simone was interested in Egyptology. Later, Stella takes the drunken Trelkovsky to her apartment, where he tells her about the tooth he found. On the bed, Stella begins to undress him, but before he falls asleep, he tells her about a man who lost an arm. He wonders when–after losing a tooth, arm, stomach or other body parts–an individual stops being who he thinks he is. At his apartment the next day, an older tenant, Madame Dioz, presents a petition for Trelkovsky to sign regarding the removal of the supposedly disruptive Gaderian and her child, whom Dioz claims is a boy, not a girl. When Trelkovsky refuses to sign the paper, Dioz becomes upset and critical of him. One day, while looking out his window, Trelkovsky notices that workmen are repairing the glass awning below and says to himself, “It is for me.” Arriving home one evening, Trelkovsky hallucinates Dioz attacking him, but his own hands are around his neck. At the police station where he is taken, the inspector warns Trelkovsky that neighbors have been complaining about him. Later, in his apartment, he paints his fingernails red with Simone’s polish. In the bathroom, he finds the walls covered with hieroglyphics and when he looks out the window toward his apartment, he sees himself looking back. Emotionally shaken, Trelkovsky returns to his apartment, and from his window, he looks back to the bathroom and sees Simone there, removing her bandages. When he awakens in the morning, Trelkovsky hears the sound of the workmen outside and looks down at them from the window. They laugh at him and when he looks in the mirror, he sees he is wearing Simone’s makeup and finds her dress draped across a chair, as if recently worn. From this he concludes that his neighbors are trying to turn him into Simone in order to drive him to suicide. Vowing to “show them,” he purchases a wig and women’s shoes. Back in his apartment, he speaks to himself in a woman’s voice, and puts on Simone’s dress and makeup. Some time later he awakens with blood on his face and discovers his tooth is missing, and again presumes his neighbors are trying to instigate his suicide. Later, as Trelkovsky leaves his apartment wearing his own clothes, Zy stops him and accuses him of bringing a woman to his apartment. At the coffee shop, Trelkovsky refuses the chocolate they serve without asking and accuses them of forcing Simone’s preferences on him. At a park later, Trelkovsky slaps a crying child, calling him a “filthy little brat.” Back at home, he sits in front of his window and watches a bouncing ball, which becomes a human head. Looking down, Trelkovsky sees the neighbors attacking Gaderian and placing a mask of his own face on her daughter. When the neighbors see him, he blocks his door and window with furniture, believing they are coming for him. He sees a hand reach through the window, but attacks it with a knife, cutting his own hand on broken glass. During the night, Trelkovsky sneaks out of the building and visits Stella. Admitting to her for the first time that he is living in Simone’s apartment, he says she jumped because of aggressive neighbors who are also trying to drive him to suicide. He tells her they are trying to turn him into Simone. Stella comforts him until he falls asleep. The next morning, after she goes to work, an older man rings her doorbell. The disturbed Trelkovsky hallucinates that the man is Zy and believes that Stella, too, is in on the plot to make him commit suicide. After wrecking her apartment and stealing money, he leaves. Paranoid, he rents a hotel room. Later he goes to a bar to ask the bartender where he can buy a gun, but is thrown out. Walking in a daze, Trelkovsky is hit by a car driven by an older couple. A crowd gathers and a doctor checks him but finds nothing broken. The delusional Trelkovsky, however, imagines the older couple is Zy and Dioz and calls them murderers. After the doctor sedates him, the couple drives him to his apartment building. Inside, Trelkovsky dresses as Simone and stands at the window, where he imagines Stella, his friends and the other tenants dressed in formal evening attire, watching and applauding him from the surrounding windows and the ground below. He jumps from the window, unseen by anyone, as no one is there. However, hearing him crash through the awning, some neighbors come outside. They find Trelkovsky, injured but still alive, lying on the sidewalk. He imagines that they are trying to attack him, and makes his way back up to his apartment, where he proceeds to jump again. Later, in the hospital, Trelkovsky’s entire body is bandaged. Through his bandages he sees himself and Stella, as they were when they visited Simone, which causes Trelkovsky, who is unable to speak, to scream in anguish.