Adapted from Ralph Spence's play, three detective buffoons try to solve a mystery of gorilla murders in the home of a wealthy man in debt.
A gorilla has murdered five people. Housekeeper Kitty (Patsy Kelly) sees its hand reaching in her window and runs to butler Peters (Bela Lugosi) and Walter Stevens (Lionel Atwill). Peters shows Stevens a note threatening death. On the phone Stevens learns he must pay $250,000. He radiograms his niece Norma Denby (Anita Louise), and she arrives with her fiancé Jack Marsden (Edward Norris). Stevens is handling her estate and shows them the note. During thunder the three detectives, Harrigan (Harry Ritz), Mulligan (Al Ritz), and Garrity (Jimmy Ritz), arrive. Peters tells Jack that his car won't start. Someone outside sees Stevens put an envelope in his safe. The detectives look around. A note thrown in says "at midnight." Stevens says it is 11:45. The gorilla is let out of its cage. The radio warns Stevens he has five minutes to live. At 12 the lights go out. When they come on, Stevens is gone. Kitty sees the gorilla's arm. Jack notices that "at midnight" was blotted at the desk. The detectives turn out the lights twice, and Garrity and Mulligan disappear from the desk chair. Harrigan turns out the lights with Kitty sitting there; but she screams, and Harrigan disappears. Kitty runs from Peters, who walks after her.
Stanger (Joseph Calleia) comes in and lets Harrigan out of the closet, saying he came to use the phone. He knocks Harrigan down and handcuffs him. Jack comes in and removes the handcuffs. Garrity and Mulligan are found bound and are released. Conway (Paul Harvey) arrives to see Stevens about his debt and says that Stevens stole money. The detectives search the cellar and find the gorilla. They run out. The gorilla attacks Norma. Jack suspects Peters. The gorilla follows Harrigan and scares Kitty. Harrigan sees it and runs upstairs. The gorilla's keeper comes in and asks where his gorilla is, saying he was hired. The radio says that Stevens is dead in the garage. The gorilla knocks Harrigan out and corners Norma. Kitty is locked in the cage, and the keeper lets her out. The keeper has the gorilla bring Norma down from the roof. Stanger tries to open the safe and hides from the gorilla. The keeper restrains the gorilla and leaves. Stanger is discovered and says he is a detective. He finds a secret passage by tracing the radio wire, and they find Stevens tied up. Conway comes in. Stanger says that Stevens wanted to kill Norma for her estate; but Stanger's hand gets hairy, and he admits he is the gorilla murderer. Stanger is captured from behind by Peters, and Stevens calls the police and says that Conway used this scheme to trap the gorilla murderer.
This combination horror-detective-comedy satirizes fear
of gorillas and incompetent detectives using a mystery plot.