When disgraced American military officer Rick Leland (Humphrey Bogart) boards a Japanese ship, he is apparently willing to turn his back on his country to become a mercenary. On the vessel, Leland meets a mysterious professor named Dr. Lorenz (Sydney Greenstreet) and the beautiful Alberta Marlow (Mary Astor). Soon Lorenz shows an interest in Leland and recruits him for a dangerous mission. As Lorenz pulls Leland into a web of international espionage, the true motives of each man remain unclear.