Chan goes to the Berlin Olympics to retrieve a stolen airplane invention and to solve two murders with the help of the German police.
At Honolulu Charlie Chan (Warner Oland) sees a plane guided by remote control that Cartwright (John Eldredge) invented. The pilot Edwards is murdered, and Chan and his young son find the plane with the device removed. Chan finds employee Miller murdered, and Hopkins (Jonathan Hale) suspects Arthur Hughes (C. Henry Gordon). Pilot Richard Masters (Allan Lane), Yvonne Roland (Katherine DeMille), and Hughes are on a boat from New York with Olympic athletes that include Lee Chan (Keye Luke). Chan, Hopkins, and Cartwright take planes and the Hindenburg blimp to meet the boat at Hamburg. Betty Adams (Pauline Moore) tells Lee that Masters is with Yvonne. Lee sees Hughes take a book from Yvonne and steals the radiogram that is from Yvonne's husband. Chan and Police Inspector Strasser (Frederick Vogeding) enter Yvonne's room, and Strasser assumes she was murdered. Hughes comes in, and Hopkins accuses him; but Chan explains she escaped. Chan catches his son Lee coming in the porthole.
Hughes prevents Chan and Lee from being shot on the train. At Berlin Hughes and Masters find that Betty's camera is empty; but Chan and Strasser find the device in Betty's room. The maid warns a car and is arrested. Betty says that Yvonne hid it while helping her pack. Betty is jealous of Masters, who goes after Hopkins. Hopkins with Cartwright puts the device in his desk; but Hughes holds him up. Chan hears a shot, and Cartwright says that Hopkins stole his invention. Hughes says he tried to buy it and that Masters had a date with Yvonne; Betty stalks out, and Masters fights with Hughes. Strasser says these things cannot happen in Berlin. Yvonne gives a package to Charles Zaraka (Morgan Wallace), but it contains a book. Chan has the device.
Zaraka invites Chan to the Olympic games, and Chan meets Yvonne too. Zaraka asks Chan for the invention. Betty sees Lee abducted. Chan says he will give the device to the U. S. War Department. Chan gets two notes to be alone without police and is taken blindfolded to Yvonne and Zaraka. Chan flips a switch on the device that is a transmitter, but Hopkins says it is the invention. Police converge. Hughes stops them from killing Chan and exposes the transmitter. Chan says the device is safe. Police enter. Hopkins is shot, and Chan says that Cartwright killed Miller, whom he had kill Edwards; Cartwright also abducted Hopkins. Chan risked Lee's life and says, "Better for Oriental to lose life than to lose face." In the final scene Lee wins a swimming race.
Swastikas were removed from the Hindenberg film, and the Berlin Olympics and the self-proclaimed efficiency of the police are the only references to the Nazis. Yet the theme is protecting military secrets, and the statement of Orientals sacrificing life rather than face foreshadows the Japanese conflict as well.