The Devil You Know by Mike Carey.  

When browsing the horror section of the Chester library, I was surprised to see two paranormals penned by Mike Carey – Carey's one of my favorite comics authors, and I've picked up just about everything by him that came across the library shelves so far. A little investigation revealed that his Felix Castor series doesn't seem to have been published in the States beyond this first title. Which is a shame because it's quite a good otherwordly exorcist book; Carey's Castor is equal parts John Constantine and Phillip Marlowe in a thoroughly creepy London. The plot of the novel follows Felix as he attempts to find the source of a haunting in a local archive, while thwarted by a demon, a were, and a succubus. Fans of Carey's tight plotting on Lucifer and Hellblazer will recognize similar ingenious twists that made his run on the titles so good. I for one, am looking forward to reading the next entry in the series.