Felix Castor is a freelance exorcist, and London is his stamping ground. At a time when the supernatural world is in upheaval and spilling over into the mundane reality of the living, his skills have never been more in demand. A good exorcist can charge what he likes, and enjoy a hell of a life-style, but there's a risk: sooner or later he's going to take on a spirit that's too strong for him. Castor has been retired for a year after a close encounter that he only just survived. But now old debts draw him back to the life he rejected, and he accepts a seemingly simple exorcism. Trouble is, the more he discovers about the ghost in the archive, the more things refuse to add up. What should have been a perfectly straightforward exorcism is rapidly turning into the Who can kill Castor first show, with demons, were-beings and ghosts all keen to claim the big prize.