A man has passed the frontier in a fast american car. He goes aboard a yacht where a young woman has lost a large sum of money gambling. After discovering the dead body of friend of his in a cabin, the man recovers the money and takes the girl away after holding up the gangsters who were aboard. On the next day, invited by a charming woman, Lemmy Caution (for it was none other than the famous detective who brought off this exploit), finds himself in the presence of Siegella, chif of a noted gang. Lemmy caution is mistaken for a rival gangster, but after several brawls in which each turn bests the other, the detective's real identity is discovered and Siegella decides to put paid to him...