Based on S. S. Van Dine's novel, a clever detective solves a complicated series of murders involving chess and nursery stories.
Detective Philo Vance (Basil Rathbone) investigates the murder of Robin and says that he was not killed by an arrow, though Sergeant Heath (James Donlan) believes that Sperling is guilty. Professor Bertrand Dillard (Alec B. Francis) saw Robin and Sperling. Vance questions Miss Drukker (Zelda Sears) about her brother Adolph Drukker (George F. Marion), who says he heard a scream and was in his room. A note arrives from the bishop. Sperling (Delmer Daves) is found and admits he took an arrow down. Vance says the bishop refers to a chess game in the archery room. Belle Dillard (Leila Hyams) gets a note to go to the park for a clue and reads stories to children, while Johnny Sprigg is shot. Vance and District Attorney Markham (Clarence Geldart) tell Erik Arnesson (Roland Young) that the murderer left a chess bishop at Miss Drukker's door. Erik says that Adolph Drukker and John Purdee (Charles Quatermaine) argued about chess. Markham tells Vance that Sperling's alibi cleared him, and he now suspects Adolph Drukker. Vance tells Sergeant Heath what he did that night by clues he sees. The hunchback Adolph Drukker is murdered on a wall, and Vance is shown a note on Humpty Dumpty. Miss Drukker is also found dead from shock.
Vance asks Purdee what he did after leaving Professor Dillard and Drukker in the park. Markham questions Erik, and Vance learns of Drukker's notebook of scientific research that was taken. Belle tells Erik she heard tapping and is afraid during thunder. Vance notes that Purdee was beaten by a black bishop in recent chess tournaments. Markham tells Heath to arrest Purdee; but Vance shows him Purdee's dead body and explains he was the Jack of the latest note, proving it was murder and not suicide by the house of cards. Professor Dillard mentions the Ibsen play The Pretenders to indicate that Erik is the bishop. Vance and Markham rush to Dillard's, while Belle hears a typewriter tapping; someone grabs her and gags her. In the attic Vance finds the typewriter. Erik appears, and Professor Dillard puts something in a wine glass; but Vance switches the glasses, and Dillard confesses he killed because he lost the affection of his niece; he wanted to eliminate everyone and frame Erik. In the final scene Vance stops Heath from drinking the poisoned wine.
This sophisticated mystery keeps the audience guessing until the motive is revealed at the end. The slow pace allows the audience time to think and absorb the somber mood.