"Hex And The City", By Simon R. Green
"Would I be right in supposing that the bad guys are once again hot on your trail and that I can expect armed invasions, mayhem and bad language at any moment?"
Another in the Nightside series, this book sees John Taylor commissioned to find out the city's origins - who created it, and what was it created for. As he and his typically oddball companions (Madman, Sinner, and Pretty Poison - a succubus demon from Hell) canvas a succession of older and older and more and more dangerous entities, it becomes apparent that not only is the answer mixed up with the mystery of who and what John's mother really is, but that there are people out there who don't want the answers to be found, and they will kill to protect their interests.
This is another very entertaining installment in the series and finally brings together several of the strands that have been running through earlier books (such as who keeps sending the Harrowing after him, and the background of Walker, who represents the Authorities in the Nightside). If you liked the others, you'll like this, although given the nature of the plot, probably not the best one to start reading them on.