Mad Prince Stefan intends to take over the world as soon as he acquires a new explosive developed at a plant owned by Barbara Hackett. By blackmailing them, Stefan wins the cooperation of Barbara's uncle and the dishonest executive, Glenville, who would like to marry Barbara. Brick McDonald, an employee of Prince Stefan's, wins Barbara's confidence and after many complications--wild chases involving motor boats, airplanes, and submarines; fights with lions; and a rescue from a threatened descent into a pit of molten steel--he frustrates Prince Stefan's plans and reveals himself as the Chief of the U. S. Secret Service.—AFI