In foggy San Francisco, tough and skeptical private detective Sam Spade and his partner Miles Archer are approached by a mysterious woman who identifies herself as Miss Wonderly. She requests their assistance in tracking down her missing sister, who she claims is involved with a man named Floyd Thursby. Enticed by her allure and the promise of a lucrative fee, they accept the case. However, that night, things take a dark turn when both Archer and Thursby are found dead. The police suspect Spade due to his affair with Archer's wife, Iva, but he maintains his innocence.

As Spade delves deeper into the investigation, he encounters an eccentric assortment of characters all with one thing in common: an obsessive desire to locate a priceless statuette — the title relic. Among these figures are the effete Joel Cairo, the corpulent Kasper Gutman, and his lackey Wilmer, as well as the bewitching Miss Wonderly, whose real name is revealed to be Brigid O'Shaughnessy. They all believe Spade possesses knowledge of the artifact's whereabouts. Entangled in a web of deceit, treachery, and murder, Spade must navigate shifting allegiances and his own code of ethics to unravel the mystery surrounding the coveted falcon.