Duds (1920)

Returning from the war front, Captain Phoebe Plunkett accepts an assignment to apprehend jewel smugglers in pursuit of the Sultana diamond. On his mission, he meets Patricia Melton, who introduces herself as a French Secret Service agent also in search of the diamond. Plunkett is in love with Olga Karakoff, daughter of a wealthy jeweler, and he soon comes to suspect that Olga's father is in league with the smugglers. However, Patricia is the true impostor, and after she discovers that the jewel is encased in a locket worn around Olga's neck, she captures Olga and the diamond. Plunkett comes to the rescue and wins both Olga and a large reward for recovering the jewel.