The sinister Dr. Fu Manchu (Boris Karloff) and his equally devious daughter, Fah Lo See (Myrna Loy), clash with a British expedition that has set out in search of Genghis Khan's tomb. Working under the guidance of Sir Nayland Smith (Lewis Stone), the English team finds ancient relics -- a mask and a sword. While the group seeks the artifacts for their archeological value, Fu Manchu and Fah Lo See regard them as mystical items that they can use to gain unstoppable power.