Jamie (Jim Sturgess) is 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: the gangs are not wearing masks. They are real demons. And when Jamie's mother is killed by them in a brutal attack, he realizes he can no longer hide away. Jamie vows vengeance and turns vigilante. But the world outside is more of a nightmare than he ever imagined. As Jamie himself says: "I open up the window and madness flies in."