U.S. Secret Service agent Truxton Darnley attires himself as a sailor and boards a schooner owned by arms smuggler Gus Olsen, who is in the employ of German spy Von Linterman to smuggle arms to German raiders in the South Seas. Truxton learns Gus’s plan to blow up the National Munitions Plant in San Francisco, just before his identity is discovery and he is thrown overboard. Washed ashore on the island of Moana, Truxton meets native girl Lurline. Promising to return to her, Truxton boards a steamer bound for San Francisco to foil the plot and soon afterwards Lurline’s father sells her into marriage with Gus. Escaping to Truxton's steamer, Lurline sails to San Francisco where Gus abducts her forcing her to dance in his Barbary Coast saloon. Truxton raids the bar, kills Gus is killed and the lovers are reunited.