During a lunchtime tryst in Phoenix, Arizona, a real estate secretary named Marion Crane discusses with her boyfriend, Sam Loomis, 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 ($323,824.52 when adjusted for inflation) 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 for an unplanned trip, 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, only to be awakened by a state patrol officer. He is suspicious about her nervous behavior but allows her to drive on. Shaken by the encounter, 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. Her transaction is all for naught—the highway patrolman sees her at the car dealership and witnesses her purchase of the newer car.
Driving on, Marion encounters a sudden rainstorm and decides to stop for the night at the Bates Motel; the proprietor, Norman Bates, invites her to a light dinner after she checks in. She accepts, but then 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 hobby of taxidermy and his life with his mother, who is mentally ill and forbids him to have a life outside of her. Returning to her room, Marion decides to go back to Phoenix to return the stolen money. She prepares to take a shower, unaware that Norman is spying on her. As she is showering, a shadowy female figure suddenly comes in and stabs her to death with a chef's knife. Norman discovers the murder and meticulously 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.