Le détective privé Philip Marlowe est engagé par le général Sternwood, un riche paraplégique, pour résoudre une affaire de chantage dont il est victime de la part d’Arthur Gwynn Geiger, un bouquiniste qui est intimement lié à sa fille Carmen. Avant son départ, Marlowe est interpellé par Vivian, la seconde fille du général, qui pense qu’il a été engagé pour retrouver son mari, Rusty Regan, disparu depuis un mois. Marlowe prend Geiger en filature, découvre que celui-ci est impliqué dans la pornographie, mais finit par le retrouver mort chez lui, avec Carmen nue et droguée. Quand il revient sur les lieux après avoir mis Carmen en sureté, le corps a disparu. Marlowe commence alors une enquête qui va s’avérer très complexe.
Private investigator Philip Marlowe is called to the home of wealthy, elderly General Sternwood. He wants Marlowe to deal with a blackmail attempt by a bookseller named Arthur Geiger on his wild young daughter Carmen. She had previously been blackmailed by a Joe Brody. Sternwood mentions his other, older daughter Vivian, who is in a loveless marriage with a man named Rusty Regan, who has disappeared. On Marlowe’s way out, Vivian wonders if he was hired to find Regan, but Marlowe won’t say.
Marlowe investigates Geiger’s bookstore and determines it is a pornography lending library. He follows Geiger home, stakes out his house, and sees Carmen Sternwood enter. Later, he hears a scream followed by gunshots and two cars speeding away. He rushes in to find Geiger dead and Carmen drugged and naked in front of an empty camera. He takes her home, but when he returns, Geiger’s body is gone and he quickly leaves. The next day, the police call him and let him know the Sternwoods’ car was found driven off a pier with their chauffeur dead inside. It appears that he was hit before the car entered the water. The police also ask if Marlowe is looking for Regan.
Marlowe stakes out the bookstore and sees its inventory being moved to Joe Brody’s home. Vivian comes to his office and says Carmen is now being blackmailed with the nude photos from last night. She also mentions going gambling at the casino of Eddie Mars, and volunteers that Eddie’s wife Mona ran off with Rusty. Marlowe revisits Geiger’s house and finds Carmen trying to get in. They look for the photos but she plays dumb about the night before. Eddie Mars suddenly enters; he says he is Geiger’s landlord and is looking for him. Mars demands to know why Marlowe is there, but Marlowe is unfazed and states he is no threat to Mars.
Marlowe goes to Brody’s home and finds him with Agnes, the bookstore’s clerk. He tells them he knows they are taking over the lending library and blackmailing Carmen with the nude photos. Carmen forces her way in with a gun and demands the photos, but Marlowe takes her gun and makes her leave. Marlowe interrogates Brody further and pieces together the full story: Geiger was blackmailing Carmen and the family driver didn’t like it, so he sneaked in, killed him, and took the film of Carmen. Brody was staking out the house too and pursued the driver, stole the film, and hit him and possibly pushed the car off the pier. Suddenly the doorbell rings and Brody is shot dead; Marlowe gives chase and catches Geiger’s male lover, who shot Brody thinking he killed Geiger. He had also hidden Geiger’s body so he could remove his own belongings before the police could get wind of the murder.
The case is now over, but Marlowe is nagged by Regan’s disappearance. The police accept that he simply ran off with Mona Mars, since she is also missing and Eddie Mars wouldn’t risk committing a murder where he’d be the obvious suspect. Mars calls Marlowe to his casino, and seems to be nonchalant about everything. Vivian is also there, and Marlowe senses something between her and Mars. He drives her home and she tries to seduce him, but he rejects her advances. When he gets home, he finds Carmen has sneaked into his bed, and he rejects her, too.
A man named Harry Jones, who is Agnes’s new partner, approaches Marlowe and offers to sell him the location of Mona Mars. Marlowe plans to meet him later, but Mars’s deadly henchman Canino is suspicious of Jones and Agnes’s intentions and kills Jones first. Marlowe manages to meet Agnes anyway and receive the information. He goes to the location, a repair shop with home in back, but Canino jumps him and knocks him out. When he awakens, he is tied up and Mona Mars is there with him. She says she hasn’t seen Rusty in months; she only hid out to help Eddie, and insists he didn’t kill Rusty. She frees him and he shoots and kills Canino.
The next day, Marlowe visits General Sternwood, who is still curious about Rusty’s whereabouts. On the way out, Marlowe returns Carmen’s gun to her, and she asks him to teach her how to shoot. They go to an abandoned field, where she tries to kill him, but he has loaded the gun with blanks. Marlowe brings her back and tells Vivian he has guessed the truth: Carmen came on to Rusty and he refused her, so she killed him. Eddie Mars, who had been backing Geiger, helped Vivian conceal it by inventing a story about his wife running off with Rusty, and then began blackmailing her himself. Vivian says she did it to protect her father, and promises to have Carmen institutionalized.