Detective Philip Marlowe probes the seedy underbelly of Los Angeles in search of a woman's missing sister.

Private investigator Philip Marlowe is hired by Orfamay Quest to find her missing brother Orrin. He visits a sleazy hotel and questions the owner and Grant Hicks, the current occupant of Orrin's room. Neither can provide any information, and the two men are soon found murdered with an icepick. Marlowe is knocked out but regains consciousness in time to see actress Mavis Wald flee from the hotel. He searches Hicks's body and finds a claim check for a camera shop, where he picks up some photographs of Mavis making love to notorious gangster Sonny Steelgrave. Marlowe tracks Mavis to her apartment and meets Dolores, a stripper and close friend of Mavis, but both prove uncooperative. In addition to a threat on his life made by Steelgrave and his henchman Wong, Marlowe is harassed by police Lieutenant French, who suspects him of murdering Hicks. Following a new lead, he calls on Dr. Lagardie and discovers the mortally wounded Orrin, who stabs Marlowe with an icepick before dying. After he is nursed back to health by Dolores, Marlowe tells Orfamay of her brother's death. At Dolores' request, he goes to Steelgrave's house and discovers Mavis, who is revealed to be Orfamay's sister, sitting next to Steelgrave's dead body. Marlowe, however, believes that Mavis is protecting her sister and lets her go. The following day, Mavis learns that Orfamay and Orrin planned to use the photographs to blackmail her. At the nightclub where Dolores works, Marlowe uncovers Lagardie's association with Dolores and telephones the police. Lagardie arrives before the police, shoots Dolores, and then kills himself.