Wilfred Glendon (Henry Hull) is a wealthy and world-renowned English botanist who journeys to Tibet in search of the elusive mariphasa plant. While there, he is attacked and bitten by a creature later revealed to be a werewolf, although he succeeds in acquiring a specimen of the mariphasa. Once back home in London he is approached by a fellow botanist, Dr. Yogami (Warner Oland), who claims to have met him in Tibet while also seeking the mariphasa. Yogami warns Glendon that the bite of a werewolf would cause him to become a werewolf as well, adding that the mariphasa is a temporary antidote for the disease.