Spade telephones Polhaus to tell them that Wilmer shot Thursby and Archer, and that Gutman and Cairo have just left the Alexandria.
Turning to Brigid, Spade asks her why she had killed Archer. After trying (unsuccessfully) to lie her way through it, Brigid finally confesses that she was hoping Archer would scare Thursby. But when that didn't work and Thursby wouldn't leave, she killed Archer to pin the crime on Thursby.
But her plan backfired when Thursby was killed by Wilmer. Brigid realized then that Gutman was in town, so she went back to Spade for protection.
Spade tells Brigid that he's turning her into the police for Archer's murder. She begs him not to, arguing that he loves her and has to help her.
Spade admits that he may be in love with her, but says that he has no choice because when your partner is killed, you can't let the murderer get away with it. He adds that the penalty for murder is likely twenty years, but if they hang her, he'll always remember her.
When the police arrive, Spade turns Brigid in. Polhaus tells Spade that when they got to suite 12-C, Gutman had just been shot and killed by Wilmer.
Spade returns to his office and tells Effie what happened. The doorbell rings, and Effie goes to answer it. The visitor is Iva.