While on a botanical expedition in Tibet Dr. Wilfred Glendon (Henry Hull) is attacked in the dark by a strange animal. Returning to London, he finds himself turning nightly into a werewolf and terrorizing the city, with the only hope for curing his affliction a rare Asian flower. London is shaken by a series of grisly murders. Suspicion falls on an attractive young woman who is rumored to have werewolves in her family tree.