Young Marion Crane (Janet Leigh) works in Phoenix and is trusted by her boss Lowery (Vaughn Taylor). Her boyfriend Sam Loomis (John Gavin) runs a hardware store in Fairvale. He cannot afford to remarry because he has to pay off his father's debts and alimony to his ex-wife, so he can only meet Marion occasionally on business trips. Marion is dissatisfied with this, so she takes the opportunity to abscond with $40,000 in public funds on Friday afternoon. However, Marion's escape is not smooth: she was first witnessed by Lowery when leaving the city, and was suspected by the police early Saturday morning. After spending $700 to exchange the old car for a new one, Marion continued to drive nervously. After nightfall, it rained heavily, the vision was blurred, and it was impossible to drive. Marion had to park the car at the Bates Motel on the side of the road. The boss Norman (Anthony Perkins) is very friendly and tries to invite Marion to his home for dinner, but is rudely stopped by the vicious mother, so he has to bring the dinner to the hotel living room. Marion talks with Norman while eating in the living room, and finally decides to return to Phoenix on Sunday. After dinner, Marion returns to her room to take a shower. At this time, an old woman suddenly appears in the bathroom...