Grisly strangulations in London alert Nayland Smith of Scotland Yard to the possibility that fiendish Fu Manchu may not after all be dead, even though Smith witnessed his execution. A killer spray made from Tibetan berries seems to be involved and clues keep leading back to the Thames.

Aliens from a dying world plot to conquer earth by preying on man's superstitions. Bringing two dead scientists back to life, they use their knowledge to re-animate various earth monsters, including the werewolf, Frankenstein's monster, the mummy Tao-Tet, and the vampire Count de Meirhoff.