Based on Joseph Kesselring's play and directed by Frank Capra, a confirmed bachelor gets married and discovers his family is full of insane murderers.
In Brooklyn, Mortimer Brewster (Cary Grant) and Elaine Harper (Priscilla Lane) apply for a marriage license; but he flees publicity because he writes against marriage. Police sergeant Brophy introduces the new officer O'Hara (Jack Carson) to the sweet Brewster sisters Abby (Josephine Hull) and Martha (Jean Adair) and Teddy (John Alexander), who thinks he is Roosevelt. Abby tells Martha of their latest victim. Mortimer has married Elaine. Teddy is digging a new lock for the Panama Canal in the cellar, and Mortimer finds a corpse in the window seat. Martha and Abby say they poisoned him with wine. Mortimer learns they plan to bury him with eleven others Teddy thinks are yellow fever victims. Mortimer makes Elaine leave and calls Judge Coleman about having Teddy committed. An old man comes to see the room, and Mortimer prevents Abby and Martha from poisoning him, explaining it is wrong. Mortimer calls Witherspoon (Edward Everett Horton) at the sanatorium.
Jonathan Brewster (Raymond Massey) and Dr. Einstein (Peter Lorre) come in to hide from the police, hoping to dispose of the man Jonathan killed. Mortimer gets Judge Coleman to sign the papers to commit Teddy. Jonathan tells his aunts that he and Einstein must stay there, and Dr. Einstein finds the hole Teddy is digging. In the dark Jonathan brings in the body through the window. Elaine comes in and is threatened by Jonathan. Teddy interrupts, and the aunts come down to let Mortimer in. He tells Jonathan and Dr. Einstein to leave, but they refuse. Mortimer says he will sleep on the window seat and calls Witherspoon while Elaine says Jonathan tried to strangle her. Mortimer finds a different body in the window seat and shows it to Abby. Mortimer realizes that Jonathan is hiding it. O'Hara arrives, and Mortimer welcomes him, telling Jonathan and Dr. Einstein to leave; but they have discovered the body in the cellar and threaten to tell. O'Hara and Mortimer go out. Abby tells Jonathan they have twelve graves and no more room. Dr. Einstein says they have equaled Jonathan in killing twelve. In the cemetery Mortimer turns Teddy over to Dr. Gilchrist. Mortimer sees Elaine in her window and says he has insanity in his family. Dr. Gilchrist signs the papers. Dr. Einstein warns Mortimer before Jonathan prepares to kill him slowly. O'Hara comes in, finds Mortimer tied up, and tells him the story of his play while Dr. Einstein knocks out Jonathan. Two policemen come in and arrest Jonathan. Mortimer watches them fight. Captain Rooney (James Gleason) comes in and says two men are wanted. Witherspoon arrives to take Teddy. Abby and Martha want to go with Teddy and sign their commitment papers. Rooney lets Dr. Einstein escape. Abby and Martha tell Mortimer he is not related to them. Mortimer kisses Elaine to keep her from telling of the twelve graves.
This macabre farce was so successful on Broadway that
release of the film was delayed three years while millions of
people in the world were working hard figuring out how to kill
each other.