Brigid O’Shaughnessy visits Sam Spade and Miles Archer, detectives, to ask them to trail Floyd Thursby. Archer, who takes the job, is murdered. Later that same night, Thursby is shot down in front of his hotel. The police suspect Spade of killing Thursby to avenge Archer’s murder. Brigid leaves word at Spade’s office that she wants to see him. She moves out of her hotel because she is afraid. At her new apartment, she says she cannot divulge the whole story, but she does tell Spade that she had met Thursby in Asia. They had arrived in San Francisco the week before. She assumes Thursby killed Archer but does not know who killed Thursby.

When Spade returns to his office, Joel Cairo is waiting. He offers Spade five thousand dollars for the recovery of a statuette of a black bird. That night, Spade is trailed by a small young man in a gray overcoat. Spade eludes him long enough to slip into Brigid’s apartment building. There, he learns that Brigid is connected in some way with a mysterious black bird, a replica of a falcon. Later they go to Spade’s apartment to meet Cairo. She tells Cairo she does not have the falcon. He will have to wait, possibly a week, before she can sell it to him.

The police learn that Spade is having an illicit affair with Iva Archer and begin to suspect Spade might have killed Archer so he could marry his partner’s wife. When the police arrive to question Spade about their new line of inquiry, they discover Cairo and Brigid in a squabble. Spade introduces Brigid as an operator in his employ and says they are questioning Cairo about the two murders. After Cairo and the police officer leave, Brigid tells Sam she does not know what makes the falcon important. She had been hired to steal it from a Russian named Kemidov in Constantinople, Turkey.

Next morning, before Brigid awakens, Spade gets groceries and then incidentally searches her apartment for the falcon, which he fails to find. He is certain Brigid knows where it is. Brigid is afraid of what Cairo might do, however, and Spade arranges for her to stay at the home of his secretary.

In explaining to Cairo how Thursby was killed, Brigid outlined the letter “G” in the air; Spade knows that special significance is attached to that letter. He confronts the youth who is trailing him and says that “G” will have to deal with him. Shortly after, a Mr. Gutman calls, inviting Spade to his hotel suite. Spade tells him that Cairo offered ten thousand dollars, not five, for the falcon. Gutman laughs derisively; the statuette is obviously worth a fortune. Pretending to be furious because Gutman will reveal no more, Spade storms out, saying he will give Gutman until 5:30 that evening to talk.

From a taxi driver, Spade learns that instead of going to Effie’s house, Brigid had hurried to the waterfront after buying a newspaper. When Gutman summons him back to his hotel suite, Spade learns that the falcon is an ancient ornament, made in Malta, encrusted with precious gems and later in its bloody history covered with black enamel to conceal its value. Gutman traced it to the Constantinople home of Kemidov, where Gutman’s agents had stolen it but had run off with it.

Next day, Spade searches Cairo’s hotel room and finds that something had been torn out of Cairo’s newspaper the day before. He buys another copy of that paper and sees that the section Cairo had torn out reports the arrival of the ship La Paloma from Hong Kong. Remembering that Brigid mentioned Asia, he associates her impromptu waterfront errand with the ship’s arrival. Later, he learns that Cairo has checked out of his hotel. Meanwhile, Spade boards La Paloma and learns that Gutman, Cairo, the strange young man, and Brigid had held a long conference with Jacobi, the captain.

While Spade is later relating his discoveries to his secretary, a man bursts in, holds out a bundle, and drops dead. Spade opens the bundle and discovers the falcon. Spade is sure that the dead man is Captain Jacobi. He has his secretary call the police while he checks the falcon at a nearby bus terminal and mails the receipt to his own post-office box. He then answers a distress call from Brigid, who claims she is being forcibly held at Gutman’s hotel suite. She is not there. Instead, Spade finds Gutman’s daughter, who sends him on a wild-goose chase. When he returns to his apartment, he meets Brigid waiting outside, obviously terrified. Opening the door, he finds Gutman, the young man, and Cairo waiting with drawn guns.

Spade realizes that his wild-goose chase had been designed to get him out of the way long enough to give these people time to find Jacobi before he returned. Spade says he will relinquish the falcon for ten thousand dollars and someone on whom to blame the murders. He suggests the young man, Wilmer Cook, as the fall guy. Spade explains that if Wilmer were hanged for Thursby’s murder, the district attorney would drop the case, taking it for granted that Jacobi had been killed by the same person. Gutman, sure that Thursby had killed Archer, finally consents to make his young bodyguard the scapegoat.

Gutman produces ten one-thousand-dollar bills. Spade calls Effie and asks her to get the claim check from the post office and redeem the falcon. After she delivers the package, Gutman unties it and finds a lead imitation. Kemidov had tricked him. Spade gives back nine thousand dollars and the men leave in haste, after discovering that Wilmer has slipped away unnoticed. Then Spade calls the police and tells them that Wilmer had killed Jacobi and Thursby and that Gutman and Cairo are accessories.

Knowing that Gutman will implicate him and Brigid in the affair, Spade makes Brigid confess that she had lured Archer into an alley that first night and had shot him with Thursby’s revolver. He tells Brigid he intends to turn her over to the police. He has to clear himself of suspicion of killing his partner and will not let a woman stand in his way.