Title: Psycho

During a lunchtime tryst in Phoenix, Arizona, a real estate secretary, Marion Crane and her boyfriend Sam Loomis discuss how they cannot afford to get married because of Sam's debts. After lunch, Marion returns to work, where a client drops off a $40,000 cash payment on a property. Her boss asks her to deposit the money in the bank, and she asks if she can take the rest of the afternoon off. Returning home, she begins to pack, deciding to steal the money and give it to Sam in Fairvale, California. She is seen by her boss on her way out of town, which makes her nervous. During the trip, she pulls over on the side of the road and falls asleep, and is woken by a state patrol officer. Suspicious about her nervous behavior, he notes her license plate number and follows her at a close distance. Hoping to shake his pursuit, Marion stops at an automobile dealership and trades in her Ford Mainline, with its Arizona license plates, for a Ford Custom 300 that has California tags.

Marion stops for the night at the Bates Motel. The proprietor, Norman Bates, invites her to a light dinner after she checks in. She accepts, but hears an argument between Norman and his mother about bringing a woman into her house. They eat in the motel parlor, where he tells her about his life with his mother, who is mentally ill and forbids him to have an independent life. Moved by Norman's story, Marion decides to go back to Phoenix in the morning to return the stolen money, and prepares for bed. As she showers, a shadowy figure stabs her to death with a chef's knife. Norman discovers the murder and assumes his mother is responsible. He cleans up the crime scene, putting Marion's corpse and her possessions—including the embezzled money—into the trunk of her car and sinking it in the swamps near the motel.

A week later, Marion's sister Lila arrives in Fairvale and confronts Sam about the whereabouts of her sister. Private investigator Milton Arbogast approaches them and confirms that Marion is wanted for stealing the $40,000. He checks the motels, and Norman's evasive and inconsistent answers arouse his suspicions. After hearing that Marion met Norman's mother, he asks to speak with her, but Norman refuses. Arbogast calls Lila and Sam to update them. He goes to the Bates' home in search of Norman's mother; as he reaches the top of the stairs, he is murdered. When Lila and Sam do not hear from Arbogast, Sam visits the motel. He finds only Mrs. Bates, who ignores his knocking. Lila and Sam go to the local sheriff, who informs them that Mrs. Bates killed herself ten years ago, and concludes that Arbogast lied to confuse them and made off with the $40,000. Convinced that some ill has befallen Arbogast, Lila and Sam make their way to the motel. Norman takes his unwilling mother from her room and hides her in the fruit cellar.

At the motel, Lila and Sam meet Norman. Sam distracts him by striking up conversation while Lila sneaks up to the house. When Sam tells Norman they have come to question his mother, he knocks Sam out and rushes to the house. Lila hides in the cellar, where she finds Mrs. Bates in a chair. Lila turns her around and discovers she is a mummified corpse. Lila screams as Norman runs into the cellar, holding a knife and wearing his mother's clothes and a wig. Before Norman can attack Lila, Sam, having regained consciousness, subdues him.

At the courthouse, a psychiatrist explains that Norman murdered Mrs. Bates and her lover ten years prior out of jealousy. Unable to bear the guilt, he exhumed her corpse and began to treat it as if she were still alive. He recreated his mother in his own mind as an alternate personality, dressing in her clothes and talking to himself in her voice. This "Mother" personality is jealous and possessive: whenever Norman feels attracted to a woman, "Mother" kills her. As "Mother", Norman killed two young girls prior to Marion, as well as Arbogast. The psychiatrist says the "Mother" personality has taken permanent hold of Norman's mind. While Norman sits in a holding cell, "Mother" protests that the murders were Norman's doing. Marion's car is pulled out of the swamp.