In 1960 Fairville, California, motel owner Norman Bates assumes the identity of his late mother, Norma, and murders guest Marion Crane. After twenty-two years in a mental institution, a judge declares Norman legally sane, based on testimony by psychiatrist Dr. Bill Raymond. However, Marion Crane’s sister, Lila Loomis, argues against Norman’s release, citing the seven people he murdered, and warning that he will kill again. Dr. Raymond returns Norman to his Victorian home, which overlooks the Bates Motel. Norman sees a woman standing in a bedroom window, but believes it is an illusion. Following the doctor’s departure, Norman finds a note under the telephone, which reads, “Norman, I’ll be home late. Fix your own dinner. Love, M.” He hears his mother’s voice and relives the moment he poisoned her. The next day, Norman begins his new job as a cook’s helper in a diner, and befriends waitress Mary Samuels. That evening, Mary is evicted from her boyfriend’s apartment, and Norman offers her a free room in his motel. However, when Norman discovers that it has become a haven for drug parties and sexual trysts, he fires manager Warren Toomey, who taunts his employer by reminding him of the murders he committed. Norman offers Mary a spare room in the house, but she is reluctant, based on his history of mental illness. Norman admits to committing matricide, but begs her to stay, saying he is afraid to be alone. As they climb the stairs, Mary insists on entering Norma’s room, telling her host that he needs to face his fears. Inside, the furniture is covered with sheets and the bed is taken apart. Norman directs Mary to her room, and she barricades the door. The next day at the diner, Mary informs Norman that she will be moving to a friend’s apartment. A drunken Warren Toomey enters and accuses Mary of being Norman’s mistress. Norman finds an order ticket with the message, “Norman, Don’t let that little whore in my house again! Love, M.” He attributes the prank to Toomey, who loudly informs fellow patrons that Norman is a serial killer, threatening him with violence. Norman holds his temper, but after Toomey leaves, he is unable to find the note. Manager Emma Spool sends Norman home for the afternoon, believing he is overwrought. Mary returns to the house that evening and accepts Norman’s invitation to stay after being kept awake by her roommate’s sexual activities. While Mary showers in the bathroom, someone watches through a peephole in the wall. Norman receives a telephone call requesting Mrs. Bates. In the motel office, a woman dressed as Norma slashes Warren Toomey with a knife. Later, Norman informs Dr. Raymond of his new housemate, and his plans to run the motel full-time. In the bathroom, Mary discovers the peephole, which faces Norma’s bedroom. After leaving the Bates home, Dr. Raymond informs Sheriff John Hunt of the notes and telephone calls Norman receives, stating that someone is trying to drive his patient insane. Meanwhile, Norman sees his mother’s silhouette in her bedroom window, and enters to find the room completely furnished. On the vanity is a note, which reads, “Norman, get rid of that slut or I’ll kill her. Love, Mother.” Norman runs to the attic and the door slams behind him, locking him in. Two teenagers sneak into the fruit cellar to have sex and become frightened by the shadow of a woman. While the girl escapes through a window, the boy is stabbed to death. When Mary releases Norman from the attic, he leads her to his mother’s room, which has been restored to its previous unlived-in state. Sheriff Hunt and Deputy Poole appear at the door, inquiring about the stabbing in the cellar. The officers find no evidence of a disturbance, and Mary assures them that Norman was with her at the time. Although Norman appreciates Mary’s gesture, he fears that his psychosis is returning. At the sheriff’s office, Hunt denies Lila Loomis’s demands for Norman’s arrest, citing the suspect’s alibi and the absence of a corpse. She advises the sheriff to drag the swamp behind the motel, where Norman used to hide his victims. Meanwhile, Mary tries to calm the distraught Norman, and searches for whiskey in the motel office, where she encounters her mother, Lila Loomis. Mary declares Norman’s innocence, and refuses to further participate in Lila’s plan to drive him insane. As Mary returns to the house, Norman finds a bloody towel clogging the toilet. Mary cleans the floor and counters Norman’s assertions that he is a murderer. As he descends the stairs, Mary sees an eye in the peephole, and retrieves a pistol from her purse. She enters Norma’s room and she looks through the hole to see an eye staring back at her. Upon hearing Mary scream, Norman runs to her defense, then searches the house for the intruder. He hears his mother’s voice saying she plans to kill Mary. Despite Mary’s insistence that the voice belonged to an imposter, Norman fears for Mary’s safety and spends the night guarding her. She awakens to find Norman standing over her with a knife, and saying that he is becoming “confused again.” Mary comforts Norman, promising to keep him from returning to the institution. In the morning, Dr. Raymond informs Norman of Mary’s relationship to Lila, blaming them for the mysterious notes and telephone calls. Norman is certain of Mary’s loyalty to him, and of his mother’s return. Dr. Raymond orders the exhumation of Mrs. Bates and proves to Norman that she is dead. Later, as Norman confronts Mary, he receives a telephone call from a woman he believes to be his real mother, rather than Mrs. Bates. Deputy Poole interrupts, summoning Norman and Mary to the swamp, where Toomey’s suitcase has been recovered. Norman claims no knowledge of Toomey’s disappearance, while Sheriff Hunt advises Mary to leave town with her mother. When Mary asks if Norman may have been adopted by Norma Bates, the sheriff assures her that they are mother and son. Moments later, Toomey’s car is dragged from the swamp, with his body in the trunk. Dr. Raymond follows Lila to the Bates home, and observes as she enters through the cellar. As she removes her “Mrs. Bates” disguise from beneath a loose stone in the floor, a woman with a knife appears and stabs Lila through the mouth while she screams. Dr. Raymond arrives and discovers the costume, but no sign of Lila. The psychiatrist shows Norman the costume, proving that Lila and Mary were impersonating Norma. However, Norman claims to have seen his real mother, referring to Mrs. Bates as his guardian. Later, Mary informs Norman of Toomey’s murder, which Norman credits to his mother, saying she is protecting him. Dr. Raymond telephones from the motel office, but Norman can only hear his mother’s voice, instructing him to kill Mary, who dons the Mrs. Bates costume and arms herself with a knife, hoping to dissuade Norman from attacking her. As Norman continues his imaginary telephone conversation, Mary pleads with him from the upstairs extension, and is grabbed from behind by Dr. Raymond. She inadvertently stabs the doctor, and as he falls down the stairs, the knife is driven deeper into his body. Norman ignores Mary’s explanation of the accident and continues his one-sided conversation, addressing her as “Mother.” Mary retrieves the knife and tries to fend off Norman, cutting him as he moves toward her. He corners her in the cellar, where Lila’s body is revealed in a pile of coal by the furnace. Believing Norman is the killer, Mary raises the knife, but is shot by police. Afterward, Sheriff Hunt attributes the murders to Lila and Mary, concluding that both women were insane. Norman returns home and is visited by his birth mother, Emma Spool, sister of Norma Bates. Emma explains that she became pregnant in her youth, and while she was institutionalized, allowed Norma to raise her son. After she admits to killing people for his protection, Norman fractures her skull with a shovel, and carries her body to Norma’s room. He talks to her as he talked to Norma, and imagines her telling him to avoid women, as none could love him as she does.