Sam Spade is a private detective in San Francisco, in partnership with Miles Archer. The beautiful "Miss Wonderley" hires them to follow Floyd Thursby, who she claims has run off with her sister. Archer takes the first stint but is found shot dead that night. Thursby is also killed later and Spade is a suspect. The next morning, Spade coolly tells his office secretary, Effie Perine, to have the office door repainted to read simply "Samuel Spade".
"Miss Wonderley" is soon revealed to be an acquisitive adventuress named Brigid O'Shaughnessy, who is involved in the search for a black statuette of unknown but substantial value. Others are after this falcon, including Joel Cairo, an effeminate criminal, and Casper Gutman, a fat man accompanied by a vicious young gunman, Wilmer Cook. O'Shaughnessy begs for Spade's protection while telling him as little as possible. They meet with Cairo at Spade's apartment, and Spade again presses O'Shaughnessy for details; again she stalls but kisses Spade. The next morning, she is asleep in his bed. Leaving her there, Spade slips out to search her apartment.
Humphrey Bogart as Sam Spade in the 1941 film adaptationEffie believes O'Shaughnessy "is all right" and Spade should help her. Effie agrees to hide her at her own home, but O'Shaughnessy disappears again. When Spade meets Gutman in his hotel room, neither will tell what he knows. Spade implies he is looking out for himself, not O'Shaughnessy. Red herrings abound. The police suspect Spade in the shootings: he was sleeping with Archer's wife, Iva. The District Attorney ties the shootings to Dixie Monahan, a Chicago gambler who had employed Thursby as a bodyguard in the Far East.
At a second meeting, Gutman tells Spade the history of the tribute of the Maltese Falcon. It was made of gold and jewels by the 16th-century Knights of Malta as a gift to the King of Spain but was captured by pirates. After passing from owner to owner, at some time it was coated with black enamel to conceal its value. Gutman traced the falcon to General Kemidov, a Russian exile in Constantinople and hired O'Shaughnessy to get it; she brought in Cairo to help. O'Shaughnessy and Thursby fled with the falcon to Hong Kong and from there to San Francisco. During this conversation, Gutman drugs Spade, who passes out on the floor.
Spade awakens alone and returns to his office where a wounded ship's captain staggers in with a package containing the falcon and dies. O'Shaughnessy calls the office, begs for Spade's help, but sends him on a wild goose chase. When he returns, O'Shaughnessy is waiting in front of Spade's apartment building. Inside Spade's apartment they find Gutman, Wilmer, and Cairo in wait with guns drawn. Gutman presents $10,000 in cash for the falcon, but Spade argues that the police must arrest someone for the murders. During a fight, Spade knocks Wilmer out, and Gutman agrees to give Wilmer to the police.
Spade has Effie fetch the falcon, but Gutman discovers it is a fake (a decoy made by General Kemidov, or possibly the falcon of legend was never real). During the excitement, Wilmer escapes. Gutman decides to go to Constantinople for the real falcon; Cairo joins him and they leave. Spade then calls the police and tells them the story, adding that he has Wilmer's guns and other evidence. While they are waiting, he bullies O'Shaughnessy into confessing her real role.
Archer was shot with Thursby's gun, but by her. She has lied to him and double-crossed him. O'Shaughnessy admits all this, but pleads that she is in love with Spade. Maybe he does care for her, Spade admits, but tells her, "I won't play the sap for you" – for personal reasons as well as needing justice for his dead partner; if she can get off with a long prison term, he'll wait for her, but if she hangs, he'll always remember her. When the police arrive, he turns her in, and the police tell him Wilmer has just shot Gutman dead.
