Plot
Trelkovsky, a quiet and unassuming man, rents an apartment in Paris whose previous tenant, Egyptologist Simone Choule, attempted suicide by throwing herself out of the window and through a pane of glass below. Before moving in officially, he meets the concierge, who shows him the apartment and the spot where Simone fell. Nobody knows the reason for the suicide attempt. Trelkovsky visits Simone in the hospital but finds her entirely in bandages and unable to talk. While still at Simone's bedside, Trelkovsky meets her friend, Stella, who has also come to visit. Stella is overwhelmed with emotion and begins talking to Simone, who looks towards her visitors and screams monstrously. The matron insists they leave, having already informed Trelkovsky that he may not speak to Simone. Trelkovsky tries to comfort Stella but dares not say that he never knew Simone, instead pretending to be another friend. They leave together and go out for a drink and a movie, where they fondle each other. Outside the theatre, they part ways. Later, Trelkovsky calls up the hospital to enquire about Simone and is told she has died.
As Trelkovsky occupies the apartment, he is chastised repeatedly by his neighbors and landlord, Monsieur Zy, for hosting a party with his friends, apparently having a woman over, making too much noise in general and not joining in on a petition against another neighbor. Trelkovsky attempts to adapt to his situation but is increasingly disturbed by the apartment and the other tenants. He frequently sees his neighbors standing motionless in the toilet room (which he can see from his own window) and discovers a hole in the wall with a human tooth stashed inside. He discusses this with his friends, who do not find things strange and belittle him for not standing up to his neighbours. He visits the apartment of one of his work friends, who plays a marching band record at a spitefully loud volume. A neighbour politely asks him to turn down the music, as his wife is ill and trying to sleep. Trelkovsky turns the record down, but his friend tells the neighbour that he will play his music as he wants, and that he does not care about his sick wife.
Trelkovsky receives a visit from one Georges Badar, who secretly loved Simone and has believed her to be alive and well. Trelkovsky updates and comforts the man and spends the night out with him. He receives a postcard that Badar had posted before realising Simone had died. Frequenting the nearby café which Simone also patronised, he is recognized as the new tenant of her apartment. The owner pressures him into having Simone's regular order, which is then always given to him without being ordered, against his preferences. They are always out of his preferred choice of cigarette, Gauloises, so he develops a habit of ordering Marlboros, which Simone used to order.
Trelkovsky becomes severely agitated and enraged when his apartment is robbed, while his neighbors and the concierge continue to berate him for making too much noise; Zy warns him not to inform the police of the burglary. Suffering from fever and bad dreams, Trelkovsky wakes up one morning to find his face made up. He buys a wig and women's shoes and goes on to dress up (using Simone's dress, which he had found in a cupboard) and the viewer realizes that no one is standing still in the opposite bathroom in front of his window. The next morning, he realizes that one of his front teeth is missing and finds it in another hole in his apartment. He suspects that Zy and the neighbors are trying to subtly change him into the last tenant, Simone, so that he too will kill himself. He becomes hostile in his day-to-day environment, and his mental state progressively deteriorates. He has visions of his neighbors playing football with a human head; finding the toilet covered in hieroglyphs; and looking across the courtyard, seeing himself standing at his apartment window, looking into the bathroom with binoculars. He runs off to Stella for comfort and sleeps over, but in the morning after she has left for work, he concludes that she too is in on his neighbors' plot and proceeds to vandalise and burgle her apartment before departing.
At night, Trelkovsky is hit by an elderly couple driving a car, but he is not seriously injured. The responding doctor, who believes Trelkovsky's odd behavior is caused by delirium tremens, gives him a sedative injection. Trelkovsky perceives the elderly couple as Zy and wife, accusing them of trying to murder him. The couple returns him to his apartment. A deranged Trelkovsky dresses up again as a woman and throws himself out of the window in the manner of Simone, before what he believes to be a clapping, cheering audience composed of his neighbors. The suicide attempt wakes up his neighbors, who call the police and attempt to restrain him. He crawls away from them back to his apartment and jumps out the window a second time moments after the police arrive.
In the final scene, Trelkovsky is bandaged up in the same fashion as Simone, in the same hospital bed. From his perspective, his and Stella's visit to Simone is shown. Trelkovsky then lets out a monstrous scream as Simone did in the earlier scene.
