Marlowe is hired by General Sternwood to follow up on a case of blackmail perpetrated by Arthur Geiger.
Marlowe finds out that Geiger is running an illegal pornography racket. He tracks down Geiger's whereabouts, only to discover that he has been shot to death in his own home, with Carmen Sternwood at the scene of the crime.
Marlowe takes Carmen back home, but when he returns to Geiger's house, his body has disappeared.
The next day, Marlowe notices that Geiger's stock of pornography is being transferred to a man named Joe Brody.
Revisiting the crime scene for a third time, Marlowe is interrupted by Eddie Mars and barely escapes without getting beaten to a pulp.
Marlowe confronts Brody and confirms that Brody had been planning on taking over Geiger's pornography operation. Brody had also tried to blackmail Vivian with naked photos of Carmen, and Marlowe retrieves the photos just before Brody is killed by Carol Lundgren.
Even though Marlowe seems to have solved the two cases of blackmail, he still continues to snoop around and a second plot begins to unfold: the disappearance of Rusty Regan.
Marlowe discovers that he's being followed by Harry Jones, who claims to have information on the whereabouts of Mona Grant, the woman who supposedly ran off with Rusty. After Jones is killed by Canino, Marlowe retrieves the information about Mona's hideout location from Agnes Lozelle.
Marlowe goes to find Mona, only to run into Canino, who knocks him unconscious. When he comes to, Marlowe discovers that he's in the same room with Mona. It turns out that Mona never ran off with Rusty, and that she had gone into hiding for the sake of her husband Eddie Mars' protection.
Marlowe shoots his way out of the house, killing Canino and making his escape with Mona.
Marlowe seems to have run out of leads to follow, so he calls on General Sternwood to say that he's done with the case. As he leaves the Sternwood mansion, he runs into Carmen and returns her gun to her.
Carmen asks Marlowe to teach her how to shoot, but then aims her gun at him in an attempt to kill him. Marlowe is then able to solve the case: Carmen was the one who killed Regan because, like Marlowe, Regan had rejected Carmen's advances.
Marlowe allows Vivian to go free as long as she gets the right medical treatment for Carmen. Marlowe also agrees to hide the truth about Rusty from General Sternwood.