General Sternwood is a wealthy retired General who has retained private detective Phillip Marlowe to resolve gambling debts that his daughter, Csrmen Sternwood, owes to bookseller Arthur Gwynn Geiger. As Marlowe is leaving the General's home, his older daughter Vivian Rutledge stops him and confides that the real reason her father has retained Marlowe is to find his young friend, Sean Regan, who mysteriously disappeared a month earlier.
Marlowe goes directly to Geiger's rare book shop and finds his assistant, Agnes Louzier, minding the shop. The bookshop is a front for an illegal operation. Marlowe follows Geiger home where he hears a gunshot and a woman screaming. Breaking in, he finds Geiger's lifeless body, and a drugged Carmen Sternwood, as well as a hidden camera with a missing cartridge. Marlowe picks Carmen up and drives her home, but when he returns to Geiger's house he discovers the body has disappeared. Later Marlowe learns they the Sternwood driver has been found dead and his car driven off a pier.
Vivian comes to Marlowe's office the next morning holding scandalous pictures of Carmen which she says she received along with a blackmail demand for money in exchange for the negatives. Marlowe returns to Geiger's book shop to find Geiger's employees packing it up. Marlowe follows a car to the home of Joe Brody, a gambler who has blackmailed General Sternwood before. He returns to Geiger's house to find Carmen there. She claims to know nothing about the myrder but then insists Joe Brody killed Geiger. They are interrupted by small-time gangster Eddie Mars, the owner of Geiger's home.
Marlowe follows Vivian to Brody's apartment where he finds Brody armed and Vivian and Agnes hiding. Carmen arrives, demanding her photographs, but Marlowe keeps the pictures sending both Sternwood daughters home. Brody admits to blackmailing both General Sternwood and Vivian then he is suddenly shot dead by an unknown assailant who flees the scene. Marliwe gives chase and apprehends the assailant, a man by the name of Carol Lundgren, who is Geiger's former driver. He killed Brody in revenge for Geiger's death, not realizing that the chauffeur killed his employer. Marlowe takes Lundgren back to Geiger's house where Lundgren has returned the body. Marlowe calls the police to the house so that they can clear up both the Brody and Geiger murders.
Marlowe pays a visit to Mars' casino where he asks about Sean Regan who is believed to have run off with Mars' wife. Mars is evasive and changes the subject, telling Marlowe that Vivian is running up gambling debts. Vivian wins a large wager and wants Marlowe to take her home. One of Mars' henchmen tries to rob Viviam but Marlowe intervenes and knocks him out. Whilst driving home, Marlowe presses Vivian about the nature of her connection to Mars, telling her he knows the big win and the attempted robbery were staged for his benefit. Vivian admits nothing and is not forthcoming with an explanation. Marlowe goes home and finds an overly flirtatious Carmen Sternwood waiting for him. She admits that she did not like Regan and also lets slip that Mars frequently calls Vivian. She attempts an obviou seduction of Marlowe who throws her out of his house. The following day Vivian tells Marlowe he can stop looking for Regan as he has been found in Mexico and she is going to see him. To emphasize the point that his services are no longer required, Mars has Marlowe beaten up.
Harry Jones is an associate of Brody's who wants to marry Agnes. He conveys an offer from her to reveal the whereabouts of Mars' wife in return for two hundred dollars. Marlowe goes to meet Jones but finds a killer hired by Mars already there attempting to find Agnes himself. The killer poisons Jones after he discloses Agnes' location but the location he has given is false. Agnes telephones the office where Jones is killed whilst Marlowe is still there and he agrees to meet with her.
Agnes tells Marlowe that she has seen Mona Mars near a town called Realto, behind an auto-repair shop. When Marlowe gets there, he is attacked by the hired killer Canino. Waking, he finds himself tied up with Mona Mars watching him. Vivian then appears as Mona angrily leaves after Marlowe tells her that Mars is a gangster and a killer. Vivian is frightened for Marlowe's life and frees him, enabling him to retrieve his car and his gun. She distracts Canino who is shot by Marlowe. As they drive back to Geiger's house Vivian tries to convince Marliwe that she killed Sean Regan.