After stealing money, a woman stops at a rural hotel off the highway in California.
In Phoenix, Arizona on Friday, December the 11th, Marion Crane and Sam Loomis are at a hotel room. Marion tells Sam that she has to get back to work and tells him the next time they meet, it should be at her and Lila Crane's house. He tells her that he wants to be with her and is tired of sweating to pay off his dead father's debts and his ex-wife's alimony. He says that in a couple of years his debts will be paid off. Marion goes back to work and asks Caroline if George Lowery is back from lunch. Caroline tells her that George is with Tom Cassidy. Caroline tells her that Lila called and said to tell her that she is going to Tucson for the weekend. George and Tom arrive from lunch and Tom starts flirting with Marion and bragging about how much money he has. He pulls out 40,000 dollars in cash, which he brought to pay for a house as a wedding gift for his daughter. Tom goes into George's office to do more drinking and George tells Marion to take the money and bring it to the bank. Marion goes home and packs a suitcase and puts the envelope full of money in her purse. As she is driving out of town, she sees George walking with Tom and George gives her a confused look. During the night she pulls over on the side of the road to sleep and is woken up by a Highway Patrol Officer. She tries to drive off, but he tells her to stop and says that she is acting suspicious. He asks to see her driver's license and after looking at it and her license plate, lets her go, but follows her for a short while.
Marion drives to Bakersfield, California and pulls into California Charlie's car dealership. She buys a newspaper and reads it to see if there is anything about stolen money. While she is reading the newspaper, the Highway Patrol Officer parks across from California Charlie's and watches her. She speaks with California Charlie and asks to trade her car in, in order to buy another. She tells him that she is in a hurry and notices that the Highway Patrol Officer is watching her. California Charlie has his mechanic inspect her car and he offers to sell her a car for an obviously high amount. Marion accepts the offer, which surprises California Charlie. She goes to the women's restroom and pulls out 700 dollars from the envelope and gives it to California Charlie. As she is driving off, she almost forgets her luggage. As she is driving she imagines the Highway Patrol Officer talking with California Charlie and George speaking with Caroline on Monday when he discovers the money is missing. It starts to rain heavily and she pulls over near Fairvale, California at the Bates Motel. She goes into the front office, but no one is inside. She looks towards the house nearby and sees what appears to be a woman walking in front of one of the windows. She honks her car horn and Norman Bates runs out of the house and tells her all their rooms are available as the highway moved and no one comes around anymore. She signs in under the name Marie Samuels from Los Angeles and he gives her the key to room 1. Norman invites Marion to eat dinner with him and then goes back to the house. Marion hears an old woman's voice yelling at Norman and accusing him of having dirty thoughts about Marion. Norman brings Marion a tray of sandwiches and they eat in his parlor. He tells her about his hobby of taxidermy and that he doesn't have any friends. He tells her that he thinks everyone is in their private trap. He continues that his mother is mentally ill and then takes offense when Marion suggests he put her in a mental institution and says everyone goes a little mad sometimes.
Marion tells Norman goodnight and accidentally tells him her real name. Norman removes a painting from the office and peeps on Marion as she is undressing. As Marion is showering, she is stabbed to death by someone with a knife. Norman, who is back at the house, starts screaming about his mother being covered in blood and runs to Marion's room. He sees her dead body and then cleans up the area, wraps Marion's body in the shower curtain and puts her body and her things in the trunk of her car. He then pushes the car into the swamp on the property and it sinks beneath the surface. A week later, Sam is writing Marion a letter as a customer is reading the ingredients off the back of an insecticide can to Bob Summerfield. Lila walks into the store and asks to speak with Sam. She asks him if Marion is there and says Marion is missing. Sam sends Bob away for lunch. Arbogast walks into the store and tells Sam that Marion stole 40 thousand dollars. He tells him and Lila that be believes Marion is in town somewhere and leaves. Arbogast starts asking around town at hotels and eventually drives up to Bates Motel. He starts questioning Norman and shows him a photo of Marion. Norman says he hasn't seen her and Arbogast starts to pick out inconsistencies in Norman's story. Arborgast looks up towards the house and sees a woman's silhouette and then leaves when Norman says he doesn't want to talk to him anymore. Arbogast calls Sam's store and asks to speak with Lila. He tells her that Marion was at Bates Motel and he was going back to the motel and will see her in an hour. He drives back to the motel and walks into the house. As he gets to the top of the stairs, someone stabs him with a knife and he falls down the stairs to his death.
Sam goes to Bates Motel and looks for Arbogast and then returns back to his store. He and Lila go to speak with Deputy Sheriff Al Chambers and he tells Al that Arbogast went to the motel to speak with the woman who lives there and Mrs. Chambers assumes he means Norman got married. He and Lila tell the rest of what happened and Al tells them he thinks Arbogast found out where Marion and the money went and went after her. Al calls Norman and Norman tells him Arbogast went to the motel and then left. Al hangs up the phone and tells Lila that Norman's mother has been dead for ten years. He tells her that Norman's mother poisoned her new husband and then herself. Norman walks to a room and says he has to take his mother away. A woman's voice angrily says she will not be put in the fruit cellar, but Norman carries a body down the stairs. The next day, Lila and Sam drive to the motel and get a room from Norman. They sneak into the room Marion was at and search it and find a piece of paper with the number 40,000 on it. Lila goes to the house while Sam goes to keep Norman occupied. She goes into Norman's mother's room and finds the bed appears to be still in use. She goes into his room and finds it has a mixture of toys and adult items. Norman and Sam get into a fight and Norman hits Sam in the head with a jar and runs to the house. Lila sees Norman running to the house and hides in the fruit cellar. She finds what appears to be Mrs. Bates sitting in a chair, but when she turns the chair around, it is the mummified corpse of Norman's mother. She screams and Norman, dressed in a dress and wig and carrying a knife charges at her. Sam grabs Norman and stops him.
Later at the County Court House, Dr. Richmond explains to Lila, Sam, Al, Deputy District Attorney Alan Deats and Chief of Police James Mitchell that he knows what happened, but it wasn't Norman who told him. He explains that Norman, as his mother, murdered not only Marion and Arbogast, but also two young women. He says that Norman became troubled after his father died and murdered his mother and her new husband when he became jealous. He then started murdering women who he became attracted to as his jealous mother. He ends the conversation by saying Norman's mother has become the dominant personality and Norman no longer exists. As Norman sits in a room, his mother's voice talks in his mind and proclaims their innocence and blames Norman.