A search is on for stolen diamonds and a government agent has been killed trying to recover them. When an unsuspecting William Beddoes arrives in Lisbon on behalf of an American bank, he is mistaken for the dead agent's replacement. Hatton-Jones of the British embassy comes to Beddoes' aid. Also taking an interest is Aurora Celeste, the dead man's lover, as well as Steve Antonio, a smuggler, who is being pursued by the law's Amy Franklin. Everyone ends up aboard a yacht belonging to Dr. Mathieson, who appears to be the mastermind of the crime and knows where the hidden diamonds are. Beddoes ends up engineering an escape for all once the gems are safely in the hands of Hatton-Jones, who turns out to be the dead agent's actual successor. Beddoes collects reward money for his efforts. He heads for home, assuming he will never see any of these people again, but Franklin schemes to make sure he'll be back.