Adapted from Frederick Jackson's play, a bishop plays detective to resolve a robbery committed to right a past wrong.
Hester Grantham (Maureen O'Sullivan) asks Red (Dudley Digges) to help her get money back her father lost. At a cathedral American Donald Meadows (Norman Foster) sees Hester praying, and she asks him to help her steal with a gun for her father. They get Red and some criminals. Guy Waller (Reginald Owen) and his wife Millie Waller (Lilian Bond) are driven in the rain by Collins (Melville Cooper) and are stopped by a punctured tire as planned. At Red's inn Donald holds them up, takes Waller's wallet and hides Millie's jewels in a pot. The Bishop of Broadminster (Edmund Gwenn) and his sister Emily (Lucile Watson) come in; he observes like a detective and finds them tied up. Waller calls the police, and the Bishop gets him to offer a reward of 1,000 pounds. Red and Frenchy (Charles McNaughton) find the bishop's card in the pot. Red calls Donald at a party. Donald makes Hester stay and goes to find the Bishop.
At home the Bishop shows Emily the jewels and wallet he is using to draw the thieves. He figures out the American went to the ball and calls there to learn it is Donald. The Bishop hides the loot. The telephone wire is cut, and the Bishop sends Brooke (Etienne Girardot) for the police. Red and Frenchy stop Brooke outside. The Bishop greets Red and Frenchy but won't hand over the jewels. Donald comes in with a gun. The Bishop gives him snuff and takes his gun. The Bishop has Emily send Brooke for Waller. Hester sneaks in and gets the gun. Emily turns out the lights, and the Bishop gets the gun. He shows the papers in Waller's wallet that prove her father's invention was stolen. Frenchy comes back with a gun. He and Red leave. Brooke brings in Waller. The Bishop urges Waller to right his wrong by signing over the invention; but the wallet is gone, and he gives the jewels back to Waller. The Bishop, Hester, and Donald go to find Frenchy.
Hester and Donald are captured, and the Bishop gets a constable; but they are gone, and the constable takes the Bishop to a mission. Frenchy knocks him out. The Bishop comes to and persuades men to go out looking. Donald and Hester are tied up, but Donald persuades Red and Frenchy. Collins brings Waller, and they meet. Waller writes a check. As the Bishop and his men arrive, Waller burns the papers. The Bishop confesses he meddled but will expose Waller. Millie objects to that and persuades her husband to pay Hester. In the final scene the Bishop burns his detective novels.
This droll mystery plays with the threat one gun can have in disarmed England; but the Bishop manages to resolve the case without violence or help from the police. Nonetheless he decides to renounce his detective hobby.