Psycho is a 1959 horror novel by American writer Robert Bloch. The novel tells the story of Norman Bates, a caretaker at an isolated motel who struggles under his domineering mother and becomes embroiled in a series of murders. The novel is considered Bloch's most enduring work and one of the most influential horror books of the 20th century.
The story was famously adapted into Alfred Hitchcock's seminal 1960 film of the same name, and also loosely adapted into the Bates Motel television series (2013–2017). Bloch later wrote three sequels, which are unrelated to any of the film sequels.
Norman Bates, a middle-aged bachelor, is dominated by his mother, a mean-tempered, puritanical old woman who forbids him to have a life outside of her. They run a small motel together in the town of Fairvale, but business has floundered since the state relocated the highway. In the middle of a heated argument between them, a customer arrives, a young woman named Mary Crane.
Mary is on the run after impulsively stealing $40,000 from a client of the real estate company where she works. She stole the money so her boyfriend, Sam Loomis, could pay off his debts and they could finally get married. Mary arrives at the Bates Motel after accidentally turning off the main highway. Exhausted, she accepts Bates' invitation to have dinner with him at his house, an invitation that sends Mrs. Bates into a jealous rage; she screams, "I'll kill the bitch!", which Mary then hears.
During dinner, Mary gently suggests that Bates put his mother in a mental institution, but he denies there is anything wrong with her; "We all go a little mad sometimes", he says. Mary says goodnight and returns to her room, resolving to return the money so she will not end up like Bates. Moments later in the shower, however, a figure resembling an old woman frightens Mary with a butcher knife, and then beheads her.
Bates, who had passed out drunk after dinner, returns to the motel and finds Mary's bloody corpse. He is instantly convinced his mother is the murderer. He briefly considers letting her go to prison, but changes his mind after having a nightmare in which she sinks in quicksand, only to turn into him as she goes under. His mother comes to comfort him, and he decides to dispose of Mary's body, belongings, and car in the swamp, and go on with life as usual.
Meanwhile, Mary's sister, Lila, tells Sam of her sister's disappearance. They are soon joined by Milton Arbogast, a private investigator hired by Mary's boss to retrieve the money. Sam and Lila agree to let Arbogast lead the search for Mary. Arbogast eventually meets up with Bates, who says that Mary had left after one night; when he asks to talk with his mother, Bates refuses. This arouses Arbogast's suspicion, and he calls Lila and tells her that he is going to try to talk to Mrs. Bates. When he enters the house, the same mysterious figure who killed Mary ambushes him in the foyer, and kills him with a razor.
Sam and Lila go to Fairvale to look for Arbogast, and meet with the town sheriff, who tells them that Mrs. Bates has been dead for years, having committed suicide by poisoning her lover and herself. The young Norman had a nervous breakdown after finding them and was sent for a time to a mental institution. Sam and Lila go to the motel to investigate. Sam distracts Bates while Lila goes to get the sheriff—but she actually proceeds up to the house to investigate on her own. There she finds various books on occultism, abnormal psychology, metaphysics and Marquis de Sade, in his bedroom. During a conversation with Sam, Bates says that his mother had only pretended to be dead, and had communicated with him while he was in the institution. Bates then tells Sam that Lila tricked him and went up to the house and that his mother was waiting for her. Bates then knocks Sam unconscious with a liquor bottle that he'd been drinking from. At the house, Lila is horrified to discover Mrs. Bates's mummified corpse on the floor, in the fruit cellar. As she screams, a figure rushes into the room with a knife—Norman Bates, dressed in his mother's clothes. Sam regains consciousness, enters the room and subdues Norman before he can harm Lila.
At the police station, Sam talks to a psychiatrist who had examined Bates, while the county highway crew is out dredging the swamp to uncover the automobiles, revealing the bodies of Mary and Arbogast; a media frenzy imagines countless additional victims to be uncovered if the swamp is further drained, but "the newspaper writers didn't have to foot the bill for such a project." Sam learns that Bates and his mother had lived together in a state of total codependence ever since his father deserted them when he was still a young child. Along the way, introverted, awkward, and filled with seething rage, Norman became a secret transvestite, impersonating his mother. A bookworm, he became fascinated with the occult, spiritualism, and Satanism. When his mother took a lover named Joe Considine, Bates went over the edge with jealousy and poisoned them both, forging a suicide note in his mother's handwriting. To suppress the guilt of matricide, he developed a dissociative identity disorder ("split personality") in the outside world. He retrieved her corpse from the cemetery and preserved it and, whenever the illusion was threatened, would drink heavily, dress in her clothes and speak to himself in her voice. The "Mother" personality killed Mary because "she" was jealous of Norman feeling affection for another woman.
Bates is declared psychotic and put in a mental institution for life. Days later, the "Mother" personality completely takes over Bates's mind; he virtually becomes his mother. However, in a double-twist ending, "Mother" reveals she had to take over, as Norman's personality was actually the murderous psychotic one, and that "she" in fact couldn't hurt a fly.