A failed screenwriter falls into a mercenary romance with a faded silent-film star.

Early one morning, police arrive at a large house on Sunset Blvd. in Beverly Hills, where a man's body floats face down in the pool: Six months earlier, while down on his luck, screenwriter Joe C. Gillis is living at the Alto Nido apartments in Hollywood, California. Joe is served with a court order commanding him to relinquish his car or pay $290 in back payments by noon the next day. Hoping to make a quick deal, Joe meets with Paramount studio producer Sheldrake to peddle a baseball/gambling picture he has written, but is turned down. While in Sheldrake's office, Joe encounters studio reader Betty Schaefer, who pans the script as formulaic. Sheldrake then refuses him a personal loan, as does his agent. Despairing, Joe makes plans to return to Dayton, Ohio, where he worked as a newspaper copy writer. While driving down Sunset Blvd., he spots the two men who are trying to repossess his car and successfully eludes them, but then has a blowout. He coasts into the driveway of a dilapidated 1920s mansion and hides the car in an empty garage. Joe then enters the house, where stoic butler Max von Mayerling orders him upstairs to consult with "madame" immediately. Joe soon discovers that he has been mistaken for a mortician, who is due to arrive with a baby coffin for "madame's" dead pet chimpanzee. Joe recognizes the faded woman as Norma Desmond, once a famous silent movie star. When she rails against modern talking pictures, Joe tells her that he is a screenwriter. Excitedly, she announces that she is planning a return to the screen in a story she is writing about the Biblical figure Salomé. When Norma discovers Joe is a Sagittarius, she is convinced of their compatibility and hires him to edit her lengthy screenplay for $500 per week and puts him up in a room over her garage. The next day, Joe awakens to find that all his belongings have been moved from his apartment, and that Norma has settled his debts. Although he is angry at Norma for her presumption, he acquiesces because he so desperately needs a job. Joe soon learns that Norma's fragile but enormous ego is supported by the scores of fan letters she still receives, and two or three times a week, Max projects her silent pictures on her living-room movie screen. As Norma and what Joe calls "the waxworks," Hollywood old-timers Buster Keaton, Anna Q. Nilsson and H. B. Warner, are playing bridge one night, two men arrive and tow away Joe's car. To appease the distraught Joe, Norma arranges for Max to refurbish her old Isotta-Fraschini, an extravagant Italian sports car. The once reclusive Norma becomes increasingly controlling. After a rain storm soaks Joe's room, she has him moved into the bedroom adjacent to hers, where her three former husbands slept. When Joe notices that none of the bedroom doors have locks, Max explains that Norma's bouts of melancholy are often followed by suicide attempts. Joe then realizes that Max has been writing Norma's fan letters so that she will not feel completely forgotten. On New Year's Eve, Norma stages a lavish party for herself and Joe, but he flies into a rage because he feels smothered. Feeling rejected, she slaps him, and he leaves the house. At a lively party at the home of his friend, assistant director Artie Green, Joe again meets Betty, who is engaged to Artie, and is excited about one of Joe's stories. Joe asks to stay for a few weeks, and Artie agrees to put him up. When he calls Max to have his things sent over, however, Max tells him that Norma slit her wrists with his razor blade. Joe returns to the house at midnight and finds Norma weeping at her own stupidity for falling in love with him. She pulls him to her and they kiss. After Norma recovers, she has the pool filled, and announces that she has sent her script to Paramount's director of epics Cecil B. DeMille, with whom she made twelve pictures. One night, Joe sees Artie with Betty at Schwab's Pharmacy. Although Betty tells him she has nearly sold one of his stories, Joe says he has given up writing, and leaves. Norma later gets a call from Paramount, but refuses to take the call because DeMille has not called her himself. Finally, Norma visits the studio unannounced. While Norma receives the long-awaited attention she craves on DeMille's set, Max learns that the earlier call was an inquiry about her car, which the studio wants to use for a film. While on the lot, Joe sees Betty, who is busy revising his story, and agrees to collaborate with her on the script in her off-hours. Norma misinterprets DeMille's pitying kindness for a deal, and a staff of beauty experts descends on her house to ready her for the cameras. Betty and Joe, meanwhile, meet repeatedly in the late evenings, and he begins to care for her, but keeps his other life with Norma a secret. One night, Max reveals to Joe that he was once an influential Hollywood director who discovered Norma when she was sixteen and made her a star. After he became Norma's first husband, she left him, but when Hollywood abandoned her, he gave up his prosperous career to return to serve her as a butler. Eventually, Norma, suspicious that Joe is involved with another woman, finds his and Betty's script and goes into a deep depression. Meanwhile, Betty receives a telegram from Artie, who is filming in Arizona, asking her to marry him immediately. She confesses her love to Joe, and he admits he wants her, too. When he arrives home that evening, however, he catches Norma calling Betty to expose him as a kept man and giving her the Sunset Blvd. address. When Betty arrives, Joe bitterly explains that he is Norma's companion. Betty urges him to leave with her immediately, but he tells her he is bound to "a long term contract with no options" and allows her to leave. He then packs, with the intention of moving back to Ohio, and returns all of Norma's gifts. Joe then tells her that there will be no film of Salomé , that the studio only wants to rent her car, and that her fans have abandoned her. Shouting that "no one ever leaves a star," Norma shoots Joe twice in the back and once in the stomach, sending him to his death in the pool. A throng of reporters and policemen surround the house, but the police are unable to get Norma out of her bedroom, until Max directs the Paramount newsreel crew to set up their equipment at the bottom of the stairs, and tells Norma that the cameras have arrived. In a state of delusional shock, Norma descends the stairs as "Salomé" while Max tells the cameramen to start rolling. At the bottom of the stairs, Norma announces, "I'm ready for my close-up, Mr. DeMille."