Psycho

Marion Crane, a real estate secretary in Phoenix, Arizona, steals $40,000 in cash from her employer after hearing her boyfriend, Sam Loomis, complain that his debts are delaying their marriage. She sets off to drive to Sam's home in the town of Fairvale, California, switching cars in Bakersfield after an encounter with a suspicious policeman. A heavy rainstorm forces Marion to stop at the secluded Bates Motel just a few miles from Fairvale. Norman Bates, the proprietor, whose Second Empire style house overlooks the motel, registers Marion (who uses an alias) and invites her to dinner with him in the motel's office. When Norman returns to his house to retrieve the food, Marion overhears him arguing with his mother about his desire to dine with Marion. After he returns, he discusses his hobby as a taxidermist, his mother's "illness" and how people have a "private trap" they want to escape. When Marion suggests that Norman should have his mother institutionalized, he becomes greatly offended and insists that she is harmless.

Marion decides to drive back to Phoenix in the morning to return the stolen money. As she showers, a shadowy figure enters the bathroom with a kitchen knife and stabs her to death. Shortly afterward, Norman is heard horrified at his mother's actions and rushes back to find Marion dead. He hurriedly cleans up the murder scene and places Marion's body, her belongings, and, unbeknownst to him, the hidden cash in her car, before sinking the vehicle in a swamp.

Marion's sister, Lila, arrives in Fairvale a week later, tells Sam about the theft and demands information about Marion's whereabouts. He denies knowing anything about Marion's disappearance. A private investigator named Arbogast approaches them, stating that he has been hired to retrieve the money. He stops in at the Bates Motel and questions Norman, whose nervous conduct, stuttering, and inconsistent answers arouse his suspicion. Arbogast examines the guest register and discovers from some handwriting in it that Marion spent a night in the motel. When Arbogast infers from things Norman says that Marion had spoken to his mother, Arbogast asks to speak to her, but Norman refuses to allow it. Arbogast leaves, finds a pay phone, and calls Lila to tell her of his suspicions and that he will go back to the motel, speak to Norman's mother, and rejoin Lila in town later. When Arbogast returns and enters the Bates' house to search for Norman's mother, a shadowy figure at the top of the stairs ambushes him and slashes him around the head. He tumbles down the stairs as the figure stabs him repeatedly.

When Sam and Lila do not hear back from Arbogast, Sam goes to the motel to look for him. Sam spots a silhouette in the house who he assumes is Norman's mother, who is unresponsive to Sam's calls. Lila and Sam alert the local sheriff, Al Chambers, who tells them Norman's mother died in a murder–suicide by strychnine poisoning ten years before. Chambers suggests that Arbogast lied to Sam and Lila so he could pursue Marion and the money.

Convinced that something happened to Arbogast, Lila and Sam drive to the motel and check in. Sam distracts Norman in the office while Lila sneaks into the Bates' house. Suspicious, Norman knocks Sam out. As Norman heads to the house, Lila hides in the fruit cellar, where she discovers the mummified body of Norman's mother. Lila screams in horror, and Norman, wearing women's clothes and a wig, enters the cellar and attempts to attack her, only to be subdued by a recovered Sam.

At the police station, a psychiatrist explains to Lila, Sam, and Chambers that Norman killed his mother and her lover out of jealousy. Unable to bear the guilt, he stole his mother's corpse and treated it as if she were still alive, then re-created his mother as an alternate personality, as jealous and possessive toward Norman as he felt about his mother. Whenever Norman was attracted to a woman, "Mother" would take over. Under the "Mother" personality, Norman killed two women before he killed Marion and Arbogast. The psychiatrist concludes that "Mother" has now completely submerged Norman's personality. Norman sits in a jail cell and hears his mother's voice stating the murders were his doing. Meanwhile, Marion's car, which contains her remains and the stolen money, is pulled from the swamp.