Sir Denis Nayland Smith (Lewis Stone) of the British Secret Service warns Egyptologist Sir Lionel Barton (Lawrence Grant) that he must beat Fu Manchu in the race to find the tomb of Genghis Khan. The power-mad Fu Manchu (Boris Karloff) intends to use the sword and mask to proclaim himself the reincarnation of the legendary conqueror and inflame the peoples of Asia and the Middle East into a war to wipe out the "white race". Sir Lionel is kidnapped soon afterward and taken to Fu Manchu. Fu Manchu tries bribing his captive, even offering his own daughter, Fah Lo See (Myrna Loy). When that fails, Barton suffers the "torture of the bell" (lying underneath a gigantic, constantly ringing bell) in an unsuccessful attempt to get him to reveal the location of the tomb.