Despite warnings that the region is dangerous, Botanist Wilfred Glendon (Henry Hull) travels to Tibet in search of the "Marifasa Lupina", a rare flower which blooms only in moonlight. Back in London, Glendon is visited by the enigmatic Dr. Yogami (Warner Oland), who tells him that a current rash of murders is the work of two werewolves. Yogami also claims that the only antidote is the blooming "Marifasa" flower, which keeps the werewolves from harming the ones they love. Glendon scoffs at Yogami's stories, until the next full moon!