Philip Marlowe searches for a missing woman in this mystery shot entirely from the detective's viewpoint.

In Los Angeles, private detective Philip Marlowe recalls the day he became involved in the infamous "lady in the lake" murder case: Frustrated over the low pay of detective work, Marlowe writes a short crime story which he submits to Kingsby Publications. While meeting with magazine editor Adrienne Fromsett to discuss the publication of his story, Marlowe learns that she has summoned him to the Kingsby offices under false pretenses. Adrienne is not interested in Marlowe's story, and instead asks him to help her find Chrystal Kingsby, the estranged wife of Derace Kingsby, the magazine's publisher. When Adrienne tells Marlowe that Kingsby's wife is a liar and a cheat and that Kingsby wants a divorce, Marlowe accuses Adrienne of trying to break up Kingsby's marriage so that she can marry him herself. Marlowe is intrigued by Adrienne's desperation, and because he is also attracted to her, he agrees to work for her. After learning that Chrystal was last seen with a playboy named Chris Lavery, Marlowe begins his investigation with a visit to Lavery's home in Bay City. Lavery invites Marlowe into his home, and calmly answers his questions before abruptly knocking the detective unconscious. Hours later, Marlowe regains consciousness in a jail cell and is taken to see Bay City police detectives Lieutenant DeGarmot and Captain Fergus K. Kane. Kane warns Marlowe not to start trouble in his district and then releases him. Marlowe later reports to Adrienne, who advises him to take his investigation to Little Fawn Lake, where the Kingsbys have a resort home and where Chrystal was last seen. Before Marlowe leaves Adrienne's office for the lake, a reporter arrives with news that Bill Chess, the caretaker at Kingsby's resort, has been arrested for the murder of his wife Muriel, whose body was found in the lake. Adrienne tells Marlowe that she fears that Chrystal may actually be the murderer as she hated Muriel and insists Marlowe go to Little Fawn Lake. Upon returning from the resort, Marlowe tells Adrienne that the body found in the lake had been there for nearly a month and that he also discovered that Muriel used the name "Mildred Havelend," and that she married the caretaker because she was being pursued by someone and needed a place to hide. Marlowe also reports that Muriel and Chrystal had a fight over a man and that he, Marlowe, had found an anklet inscribed with the words, "to Mildred from Chris." Suspecting that Lavery is tied to the disappearance of both Muriel and Chrystal, Marlowe pays another visit to Lavery's house. There he finds the door unlocked and meets a confused woman wielding a pistol, who introduces herself as Mrs. Falbrook, Lavery's landlady. Mrs. Falbrook says Lavery is not in the house and that she found the gun on the landing and gives it to Marlowe before departing. The detective then investigates upstairs and in the bedroom discovers a handkerchief with the initials "A. F." on it and in the bathroom he finds Lavery's bullet-ridden body in the shower. Believing that either Adrienne or Kingsby is responsible for Lavery's murder, Marlowe interrupts a Christmas party at Kingsby's office and shows Adrienne the gun, but she appears genuinely stunned over Lavery's death. When Marlowe brings Kingsby up to date on his activities, the publisher expresses shock that Adrienne has been trying to sabotage his marriage and tells her she misunderstood his interest in her. Though she confesses that she was after Kingsby's money, Adrienne denies Marlowe's accusation that she murdered for it or that she was involved with Lavery. Adrienne then angrily fires Marlowe, but Kingsby immediately hires him to find Chrystal and help him protect her from false murder charges. Marlowe goes back to Bay City to return the gun to Lavery's and finds Kane and DeGarmot there. When left alone with DeGarmot, Marlowe suggests the policeman knows Muriel well and that he could be the man from whom she was hiding. DeGarmot scuffles with Marlowe and the police try unsuccessfully to have the detective charged with Lavery's murder. Later, Marlowe gets information from a newspaper editor contact that Muriel, a nurse, was mixed up in the mysterious death of Florence Elmore, the wife of the doctor for whom she worked in Bay City. After questioning Florence's frightened parents and learning a policeman is involved, Marlowe begins to suspect that it is Chrystal, not Muriel, whose body was found in the lake and that Muriel is the murderer and DeGarmot is covering up for her. Before he can investigate further he is attacked, but before passing out, he phones Adrienne for help and wakes up in her apartment. Adrienne admits she has fallen in love with Marlowe and they spend the day together. Later, Kingsby arrives, looking for Marlowe to tell him that he has received a telegram from Chrystal, indicating that she is in Bay City and in need of money. Marlowe suspects a trap and volunteers to deliver the money to her himself. After leaving a trail for the police to follow, Marlowe discovers that the woman who is trying to collect money from Kingsby is the same woman who introduced herself to him as Mrs. Falbrook. Marlowe realizes that Mrs. Falbrook is really Muriel and that his suspicion that she killed Chrystal and Lavery to cover up her murder of Florence is correct. When Muriel threatens Marlowe with a gun, DeGarmot arrives unexpectedly and threatens to kill both of them and frame them for all the murders. DeGarmot reveals he has been covering up for Muriel who professed romantic interest in him to get him to cover up Florence's murder. Furious at her deceit, Degarmot shoots Muriel, but as he is about to kill Marlowe, he is shot dead by Kane. With the murder case solved, Marlowe resumes his romance with Adrienne.