The Werewolf of London: 1935
Universal Pictures
Black and White
aka Unholy Hour

Director: Stuart Walker
Cast: Henry Hull, Warner Oland

Plot: A renowned botanist searches for a rare Tibetan flower and must defend himself from a howling monster.  Back in London he is told the flower is the only antidote for keeping werewolves from harming the ones they love.  He disbelieves until the next full moon.