From publicity material: The Black Tattoo unites an unlikely group whose fortunes become inexorably intertwined on one fateful day. In a chance meeting with a member of an ancient brotherhood, fourteen-year old Charlie Farnsworth and his best friend Jack Farrell manage to land themselves in the midst of an age old struggle to protect the world form an evil demon. Things go awry when Charlie learns that, rather than possessing superpowers, he has been possessed by the demon. In the sequence of events that follow, Charlie, Jack and Esme--a young member of the brotherhood--all manage to land themselves deep within the caverns of Hell, preparing for the ultimate battle of, and for, their lives.

(Source: Razorbill)