In San Francisco in 1941, private investigators Sam Spade and Miles Archer meet prospective client Ruth Wonderly. She claims to be looking for her missing sister, who is involved with a man named Floyd Thursby. Archer agrees to follow her that night and help get her sister back.
Spade is awakened by a phone call early in the morning and the police inform him that Archer has been killed. He meets his friend, Police Detective Tom Polhaus at the murder scene and then tries calling his client at her hotel, but she has checked out. Back at his apartment, he is grilled by Polhaus and Lieutenant Dundy, who tell him that Thursby was also murdered the same evening. Dundy suggests that Spade had the opportunity and motive to kill Thursby, who likely killed Archer. Archer’s widow Iva later visits him in his office, believing that Spade shot his partner so he could have her.
Later that morning, Spade meets his client, now calling herself Brigid O’Shaughnessy. She explains that Thursby was her partner and probably killed Archer, but claims to have no idea who killed Thursby. Spade distrusts her, but agrees to investigate the murders.
At his office, Spade meets Joel Cairo , who first offers him $5,000 to find a “black figure of a bird”, then pulls a gun on him in order to search the room for it. Spade knocks Cairo out and goes through his belongings. When Cairo comes round, he hires Spade. Later that evening, Spade tells O’Shaughnessy about Cairo. When Cairo shows up, it becomes clear that Spade’s acquaintances know each other. Cairo becomes agitated when O’Shaughnessy reveals that the “Fat Man” is in San Francisco.
In the morning, Spade goes to Cairo’s hotel, where he spots Wilmer, a young man who had been following him earlier, and gives Wilmer a message for his boss, Kasper Gutman. When Spade goes to meet Gutman, alias the “Fat Man”, in his hotel suite, Gutman will only talk about the Black Falcon evasively, so Spade pretends to throw a temper tantrum and storms out. Later, Wilmer takes Spade at gunpoint to see Gutman. Spade overpowers him, but meets Gutman anyway. Gutman relates the history of the Maltese Falcon, then offers Spade $25,000 for the bird and a quarter of the proceeds from its sale. After Spade passes out because his drink is spiked, Wilmer and Cairo come in from another room and leave with Gutman.
On coming round, Spade searches the suite and finds a newspaper with the arrival time of the freighter La Paloma circled. He goes to the dock, only to find the ship on fire. Later, the ship’s captain, Jacobi, shot several times, staggers into Spade’s office before dying. The bundle he was clutching contains the Maltese Falcon.
O’Shaughnessy calls the office, gives an address, then screams before the line goes dead. Spade stashes the package at the bus terminal, then goes to the address, which turns out to be an empty lot. Spade returns home and finds O’Shaughnessy hiding in a doorway. He takes her inside and finds Gutman, Cairo, and Wilmer waiting for him, guns drawn. Gutman gives Spade $10,000 for the Falcon, but Spade tells them that part of his price is someone he can turn over to the police for the murders of Thursby and Captain Jacobi, suggesting Wilmer. After some intense negotiation, Gutman and Cairo agree and Wilmer is knocked out and disarmed.
Just after dawn, Spade calls his secretary, Effie Perine, to bring him the bundle. However, when Gutman inspects the statuette, he finds it is a fake and Wilmer escapes during the tumult. Recovering his composure, Gutman invites Cairo to return with him to Istanbul to continue their quest. After they leave, Spade calls the police and tells them where to pick up the pair. Spade then angrily confronts O’Shaughnessy, telling her he knows she killed Archer to implicate Thursby, her unwanted accomplice. She confesses, but begs Spade not to turn her over to the police. Despite his feelings for her, Spade gives O’Shaughnessy up.