The Devil You Know: Mike Carey

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.
After a year spent in 'retirement' Castor is reluctantly drawn back to the life he rejected and accepts a seemingly simple exorcism case - just to pay the bills, you understand. Trouble is, the more he discovers about the ghost haunting the archive, the more things don't 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.
But that's OK; Castor knows how to deal with the dead. It's the living who piss him off.