Norman Bates, a middle-aged bachelor, is dominated by
his mother, an old woman who forbids him to have a life outside of her. They run a small motel in the town of Fairvale, but business has suffered since the state relocated the highway. Meanwhile,
Mary Crane, a young woman, is on the run after stealing $40,000 from a client of the real estate company where she works. She stole the money so her boyfriend, Sam Loomis, could pay off his debts and they could get married. Mary arrives at the Bates Motel after accidentally turning off the main highway. After checking in, she accepts Bates's invitation to have dinner with him at his house, an invitation that sends Mrs. Bates into a jealous rage. During dinner, Mary suggests that Bates put his mother in a
mental institution, but he denies that there is anything wrong with her. Mary says goodnight and returns to her room, resolving to return the money so she will not end up like Bates. However, a figure resembling an old woman later beheads Mary in the shower with a
butcher knife. Bates, who had passed out drunk after dinner, returns to the motel and finds Mary's corpse. Convinced that his mother killed her, Norman considers letting her go to prison, but changes his mind after having a nightmare in which she sinks in
quicksand, only to turn into him as she goes under. His mother comes to comfort him, and he decides to dispose of Mary's body, belongings, and car in the swamp. Meanwhile, Mary's sister,
Lila, tells Sam of her sister's disappearance. They are soon joined by Milton Arbogast, a private investigator hired by Mary's boss to retrieve the money. Arbogast eventually meets Bates, who says that Mary left after one night; when he asks to talk with his mother, Bates refuses. This arouses Arbogast's suspicion, and he calls Lila to say that he is going to try to talk to Mrs. Bates. When he enters the house, Mary's killer ambushes him in the foyer, and murders him with a razor. Sam and Lila go to Fairvale to look for Arbogast, and meet with the town sheriff, who reveals that Mrs. Bates has been dead for years, having committed suicide by
poisoning her lover and herself. The young Norman had a
nervous breakdown after finding them and was sent for a time to a mental institution. Sam and Lila go to the motel to investigate. Sam distracts Bates while Lila goes to get the sheriff, but she proceeds up to the house to investigate on her own. She finds books on
occultism,
abnormal psychology,
metaphysics, and
Marquis de Sade in his bedroom. During a conversation with Sam, Bates says that his mother had only
pretended to be dead and had communicated with him while he was in the institution. Bates then says that Lila tricked him and went up to the house, and that his mother was waiting for her. Bates knocks Sam unconscious with a liquor bottle that he has been drinking from. At the house, Lila discovers Mrs. Bates' mummified corpse on the floor in the fruit cellar. As she screams, a figure rushes into the room with a knife—Norman Bates, dressed in his mother's clothes. Meanwhile, Sam, who had regained consciousness, enters the room, and subdues Norman before he can harm Lila. Later, with Bates arrested, the county highway crew starts dredging the swamp to uncover the automobiles, revealing the bodies of Mary and Arbogast; a
media frenzy imagines additional victims to be uncovered if the swamp is further drained. It is revealed that Bates and his mother lived together in a state of total
codependence ever since his father deserted them when he was still a young child. Along the way, introverted, awkward, and filled with rage, Norman became a secret
cross-dresser, impersonating his mother. A bookworm, he became fascinated with the
occult,
spiritualism, and
Satanism. When his mother took a lover named Joe Considine, Bates went over the edge with jealousy and poisoned them both with
strychnine,
forging a suicide note in his mother's handwriting. To suppress the guilt of
matricide, he developed an
alternate personality—his mother, who is as cruel and possessive as the real Mrs. Bates had been. He retrieved her corpse from the cemetery and preserved it, and whenever the illusion was threatened, he would get drunk, dress in her clothes, and speak to himself in her voice. The "Mother" personality killed Mary because "she" was jealous of Norman's feeling of affection for another woman. Bates is declared
psychotic and put in a mental institution for life. Days later, the "Mother" personality completely takes over Bates's mind. "She" blames Norman for the murders, and is resolved to stay quiet and still to show Norman's doctors at the institution that she "wouldn't even harm a fly." ==Allusions==