In a Phoenix hotel room on a Friday afternoon, Marion Crane (Janet Leigh) and her out-of-town lover Sam Loomis (John Gavin) end a stolen lunchtime interlude with yet another disagreement about their future. Marion wants to marry Sam, but debts inherited from his father and his own alimony payments do not leave him enough money to support her as he would like. As they have done so often before on Sam's business trips to Phoenix, they part leaving their future uncertain.

Marion returns to the real estate office where she works as a secretary, arriving just ahead of her boss Mr. Lowery (Vaughn Taylor) and his client Cassidy (Frank Albertson) who buys a house from Lowery with $40,000 in cash. Lowery tells Marion to put the money in the safe deposit box at the bank until Monday. Pleading a headache, Marion asks to take the rest of the day off after her errand to the bank.

But Marion doesn't go to the bank. On the spur of the moment, she decides to keep the money, packs a suitcase, and starts driving out of town in her black Ford sedan, only to be spotted by her boss at an intersection where he gives her a suspicious look. Worried that she has been found out already, she still proceeds out of town on her way to Fairvale, California, where Sam lives. All the while she keeps looking in her rear view mirror, fearful that she's being followed. She drives well into the night and parks alongside the road to sleep.

In the morning, a highway patrolman (Mort Mills) stops to investigate her parked car, and awakens her. Startled and nervous, she arouses the patrolman's suspicions. He looks at her driver's license, taking note of the license plate number. He allows her to go on, but follows her for a while, which intensifies Marion's agitation.

Realizing that her car can easily give her away, Marion decides to trade it in for a different car. She stops in at a used car lot, hurriedly pays the salesman (John Anderson) $700 cash for a white Ford sedan, and completes the deal as the same highway patrolman watches from across the street. Nervous, she drives away and continues toward Fairvale.

As night falls on this second night, with her fears of pursuit crowding in around her, she drives into a rainstorm. Unable to see the road clearly, she spots the lighted sign of the Bates Motel, and decides to take a room for the night. As there are no other cars there, and no one in the motel office, she honks her horn upon seeing a light on in the house behind the motel, and a silhouette in the window; a young man soon comes down the path to greet her, and he introduces himself as Norman Bates (Anthony Perkins). He is a soft-spoken and shy young man who tells Marion that he lives in the large house with his mother. The motel seldom has guests anymore since the new interstate bypassed the local highway, and Marion realizes that she probably took a wrong turn in the storm. Still nervous about being tracked by the police, Marion registers under a false name "Marie S