Private detective Philip Marlowe arrives at the wealthy Sternwood family’s mansion. As Marlowe stands in the impressive hallway, Carmen Sternwood approaches him and begins to flirt. The straight-faced butler, Mr. Norris, soon leads Marlowe to a sweltering greenhouse, where the elderly General Sternwood sits in his wheelchair.
Sternwood talks warmly of his missing son-in-law Rusty Regan, but that’s not why he’s called on Marlowe. Sternwood is “being blackmailed again,” this time by Arthur Geiger, who claims Carmen owes him gambling money. The General decides to hire Marlowe to see what Geiger is up to, rather than just pay out. Once Marlowe is finished with the General, Mrs. Regan, the General’s older daughter, has Mr. Norris bring Marlowe to her elegant sitting room. She is under the impression her father has hired Marlowe to find her husband, Rusty; Marlowe provides no information either way, and considers Mrs. Regan “trouble.”
The detective goes to the rare bookstore noted on Geiger’s business card, which he quickly discovers is a front for pornographic books and is guarded by the attractive Agnes Lozelle. Marlowe stakes out Geiger’s store, and after Geiger appears, Marlowe tails him back to his house. There, Marlowe sees Carmen arrive and enter the house.
While staking out the house, Marlowe sees a flash of light and hears a scream from inside. Three gun shots ring out, followed by the sound of someone fleeing out of the back of the house. Marlowe breaks into the house through a window to find Carmen, naked and drunk but unharmed, and Geiger dead on the floor. Marlowe also finds a camera, but the plate holder has been stolen. Unable to rouse a now sleeping Carmen, Marlowe drives her home in her own car. After leaving Carmen in the hands of Mr. Norris and the maid Mathilda, Marlowe walks back to Geiger’s place. Geiger’s body is gone.
The following morning, the papers make no mention of Geiger, meaning the police are still unaware of the murder. Chief Investigator Bernie Ohls, who had originally put Marlowe in contact with the General, calls Marlowe to tell him one of the Sternwoods’ Buicks is being fished out of the sea near Lido pier, with a body inside. Ohls takes Marlowe to go see for himself, telling him that the dead man in the Buick is not Rusty Regan (having assumed that Marlowe is trying to find Rusty). The body is that of the Sternwoods’ young chauffeur, named Owen Taylor. It is unclear whether his death is the result of murder or suicide.
Ohls drops Marlowe back in town, where the detective discovers that Geiger’s books are being hauled out of his store and put into a moving truck. Marlowe hires a cab to tail the truck, which arrives at an apartment; Marlowe deduces from the mailbox outside that the apartment is that of Joe Brody. Marlowe then takes the cab back to his offices, where Mrs. Regan is waiting.
Mrs. Regan tells the detective that Carmen is being blackmailed for the incriminating photos from the missing plate in Geiger’s camera. The two discuss Rusty’s disappearance as well as the death of Owen Taylor, who was in love with Carmen. After Mrs. Regan leaves, Marlowe drives back to Geiger’s house, where he finds Carmen. When Marlowe asks her about the previous night, Carmen blames Joe Brody for killing Geiger. To himself, Marlowe questions her motives. While they are talking, the gangster Eddie Mars arrives. He and Marlowe size each other up, with Mars revealing that he owns Geiger’s house and demanding Marlowe keep his name out of any reports.
Marlowe returns to Joe Brody’s apartment, where Brody pulls a gun on the unarmed Marlowe. Agnes is there as well, and Marlowe questions them about their move to steal Geiger’s racket. Brody admits to taking the books, but denies the murder. Marlowe works out that Brody has the pictures from the camera he found in Geiger’s house. Suddenly, the door bell rings. Brody answers the door to see Carmen, who instantly points a gun to his face and demands her pictures. After a confused tussle, Marlowe manages to grab both Brody and Carmen’s guns. Brody hands Marlowe the pictures, and Carmen skips off while Marlowe stays to question Brody and Agnes. Brody admits to tailing Geiger the previous night. He says he was staking out the back of Geiger’s house as the Sternwoods’ chauffeur Owen Taylor broke in and shot Geiger. Brody then tailed the fleeing Taylor, overpowered him, and took the camera plate, before Taylor drove off, presumably to the pier.
The doorbell rings again. Brody answers and is instantly shot dead by the man on the other side. Marlowe chases after the murderer and catches him: it is Carol Lundgren, a boy Marlowe recognizes from Geiger’s store. Marlowe quickly determines this is a misplaced revenge killing. Marlowe makes Lundgren drive to Geiger’s place, where he calls chief investigator Ohls to the crime scene. They find Geiger laid out on a bed in a locked room. Ohls and Marlow ethen drive Lundgren to District Attorney Taggart Wilde’s house. Ohls and Marlowe explain the situation to Wilde, and give city cop Captain Cronjager their direct assessment of his negligent police work. Cronjager leaves with Lundgren in custody.
When Marlowe gets back to his apartment, Mars calls to confirm that his name was kept out Marlowe’s report to the police—Marlowe confirms it was. The detective then rings the Sternwoods, telling Mr. Norris to inform Mrs. Regan that the pictures have been taken care of. The next morning, Marlowe looks over the newspapers, and sees the events of the last few days have been mostly covered up; the Sternwoods are not mentioned at all.
Marlowe next goes to see Captain Al Gregory of the Missing Persons Bureau for details on Rusty, saying he wants to rule Rusty out of the blackmail case. It seems Rusty ran off with Eddie Mars’s wife, Mona, who is also missing. Gregory says he doesn’t think Eddie is involved, because he’s too business minded to act out of jealousy. A “gray Plymouth sedan” later tries to surreptitiously follow Marlowe, who loses it.
That night, Marlowe visits on Eddie Mars at his casino, the Cypress Club. Mars greets the detective warmly and invites him into his office. There, Mars offers Marlowe money for keeping his name out of the police report, but Marlowe refuses to accept it. The two discuss Rusty’s disappearance. Marlowe asks Mars if he’s responsible for the car tailing him, which shocks and worries Mars. The detective wanders into the main casino, where he finds Mrs. Regan. Marlowe drives her home. On the way, Marlowe asks her what secret Mars is holding over her, but she avoids the topic. Mrs. Regan tells Marlowe to pull over and tries to seduce him. He kisses her but refuses to take her back to his apartment, asking again what Marlowe has on her. Angry, she demands to be taken home.
When Marlowe gets back to his own apartment, Carmen is waiting for him in his bed, naked. He threatens to throw her out, and she leaves, furious. In the morning, Marlowe sees the gray Plymouth that had tailed him, and confronts the driver, inviting the “small” man up to his office. The man introduces himself as Harry Jones, a grifter, and offers Marlowe the location of missing Mona Mars in exchange for $200. Jones says that Agnes Lozelle told him she saw Mona driving in the hills above L.A., being watched by Eddie Mars’s man Lash Canino.
Marlowe thinks on it for the rest of the day before deciding to follow up on the offer. He drives to Jones’s office, where, after sneaking in, he overhears Canino questioning Jones about Agnes. Jones drinks whiskey that Canino pours him, and then Marlowe hears Jones die. Canino leaves, unaware of Marlowe’s presence. Marlowe smells cyanide on Jones’s corpse. Agnes calls the office and Marlowe arranges a meeting. Half an hour later, Marlowe hands the $200 over to Agnes, who tells him exactly where Mona is.
It is raining heavily as Marlowe drives to the hiding place. He loses control of his car, driving into the curb and bursting two tires. Luckily, he’s within walking distance of a repair garage Agnes had described. He talks his way in, and sees Canino there with Art, the garage owner. The two men jump Marlowe and knock him out. Marlowe wakes up on a sofa, handcuffed and watched by Mona. He talks her around to helping him escape. Marlowe then retrieves his gun from his now repaired car—repaired as a spare getaway, he supposes—and sees Canino driving back to the house. He lures Canino back out of the house by starting Canino’s own car engine. When Canino comes out with holding a gun to Mona’s back, Marlowe shoots Canino four times, killing him.
The next day, in his apartment, Marlowe thinks over the previous night—calling Ohls, driving with Mona to District Attorney Wilde’s house, and telling them everything. Eddie and Mona claimed they didn’t want to be in the spotlight over Rusty’s disappearance, and the police let it slide. Back in the present, Marlowe goes to talk it all over with General Sternwood. Marlowe tells the General that Geiger was trying to find out if the General was scared about something else, applying a little pressure to see how much he could really blackmail him for.
In front of the mansion, Carmen asks Marlowe to teach her to shoot. They drive down to an isolated location together. Marlowe gives her a gun and sets up the targets. Carmen shoots him five times, but he has loaded the gun with blanks. She faints, foaming at the mouth. Marlowe drives Carmen back up to the house and confronts Mrs. Regan with his theory: Carmen tried to shoot him because he turned down her sexual advance, as Carmen also most likely did with Rusty—except Rusty’s gun wasn’t filled with blanks. Marlowe tells Mrs. Regan she must have helped Carmen cover it up and asked Eddie Mars to help them, who came up with an elaborate cover story. Mrs. Regan admits everything and offers Marlowe hush money, as she doesn’t want her father to find out. Marlowe turns down the money with disgust and tells Mrs. Regan to send Carmen to a mental institution, or he will go to the police. Marlowe leaves to go to a bar, where he will think about death, “the nastiness,” and Mona.