The story follows Jamie, a troubled young man with a birthmark on his face, which has left him feeling isolated and fearful, hiding from the world outside. He lives in the East End of London, an area notorious for its violent hooded gangs. According to news reports, the gangs are now wearing demon masks. But, one night, Jamie discovers the terrifying truth.
Two scriptwriters argue about the fate of Henrietta, a charming and gamine shopgirl. One favors a comical path for their heroine, who is overcome with sentimental love for a young photographer on Bastille Day. The other has a more thrilling and dastardly fate in mind for her. Among the film's irresistible conceits is Hildegarde Neff as an oversexed circus bareback rider.