Psycho

In Phoenix, Arizona, real estate secretary Marion Crane embezzles $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 rainstorm forces Marion to stop at the secluded Bates Motel a few miles from Fairvale. Norman Bates, the proprietor, whose 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 returning, he discusses his hobby as a taxidermist, his mother's "illness", and how everyone is in a "private trap" they cannot escape. When Marion suggests that Norman should have his mother institutionalized, he becomes agitated 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. Moments later, Norman runs to the motel 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. Arbogast, a private investigator, approaches them, stating that he has been hired to retrieve the money. He stops at the Bates Motel and questions Norman, whose nervousness 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 his conversation with Norman that Marion had spoken to his mother, Arbogast asks to speak to her, but Norman refuses. Arbogast leaves and calls Lila to tell her of his suspicions. When he returns and enters the Bates' house to search for Norman's mother, a shadowy figure at the top of the stairs stabs him to death.
When Sam and Lila do not hear back from Arbogast, Sam goes to the motel to look for him. Sam spots a silhouette in a second-floor window of the house and assumes it 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 killed herself and her lover with strychnine poisoning 10 years earlier. 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 and discovers the mummified body of Norman's mother. Lila screams in horror, and Norman, wearing a dress and a wig, enters the cellar and attacks her with a knife, only to be subdued by a recovered Sam.
At the police station, a psychiatrist explains to Lila, Sam, and Chambers that Norman murdered his domineering 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 she had been in life. 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 and that she would never be suspected. Marion's car is towed from the swamp.