Richard Duvall is a young American detective in the employ of the French Secret Police. While in Paris he meets Grace Ellicot, also an American, with whom he falls in love. He marries her and is about to start on his honeymoon when he is called on by Mons. Lefevre, chief of the secret police. The French Ambassador to England, Monsieur De Grissac, has lost an ivory snuff box which must be found.