Based on a Dashiell Hammett story, Nick Charles solves two murders while his wife avoids jealousy and helps raise their child.
Col. MacFay (C. Aubrey Smith) invites Nora Charles (Myrna Loy) and Nick Charles (William Powell) for the weekend. Nick sees a body on the road, but it disappears. McFay says that Phil Church (Sheldon Leonard) is dreaming of his death. McFay's dog is killed. Dudley Horn (Patric Knowles) is engaged to Lois McFay (Virginia Grey) and tells Nick of McFay's shady deal. McFay's secretary Freddie (Tom Neal) argues with McFay and likes Lois. Nick finds a cop watching Church's house. Church tells Nick his family may be killed too, and Nick socks him. Dum-Dum (Abner Biberman) throws a knife, and Smitty (Muriel Hutchison) pulls a gun. Diamond Back Vogel (Don Costello) gives Smitty a message from her husband in prison. Church kisses Smitty. Lois comes to talk with Nick and Nora at night, and a shot is heard. McFay is found murdered by a knife. Police look for Church and Dum-Dum. Freddie and Nora are questioned. Assistant District Attorney Van Slack (Otto Kruger) questions Nick. The dog Asta finds the knife. Lois runs to Nick and is shot at by Dudley, who is killed. Van Slack asks Lois about Dudley, who was rejected by her father and was Church's enemy.
Lois hears housekeeper Mrs. Bellam (Phyllis Gordon) say she is her mother. Nick gets a threatening call and goes with Van Slack without Nora to see Smitty. Lt. Guild (Nat Pendleton) says that Smitty was there but suspects she set up the alibi. Vogel arrives, and Nick says he saw him watching Church's house. Lt. Guild and Van Slack run after Dum-Dum. Nick goes to a West Indies nightclub and finds Nora surrounded by men trying to locate Dum-Dum, who comes in and asks Nick where Church is. A man tells Nick about Church until Dum-Dum hits him.
Nick looks for Church's previous girl-friend in the apartments managed by Mrs. Dolley (Marjorie Main). While Nora asks for a room, Nick finds a bullet hole and water. Two men with guns come in the window but are arrested by Lt. Guild and his men. Ex-cons give a birthday party for the Charles' child. Church warns Nora to get Nick out of town; but Church is shot dead. Nick tells Vogel to wait. Lt. Guild holds Dum-Dum and Smitty, who accuses Vogel. Nick tells Van Slack that Church planned to be acquitted with an alibi so he couldn't be tried again. Vogel says Church was in his gambling place with bankers not wanting to testify. Nanny Dorothy (Ruth Hussey) is brought in and admits she was in prison. Nick proves that the shot was delayed with a water device and accuses Lois of killing her father to get his money sooner and of killing Church too. Lois tries to use their baby to escape; but the child is found, and Lt. Guild arrests Lois.
The wit and sophistication of Nora and Nick Charles add charm to this complicated mystery.