From Wikipedia..
The Nightside
Something from the Nightside (New York, Ace 2003), ISBN 0441010652
Agents of Light and Darkness (New York, Ace 2003), ISBN 0441011136
Nightingale's Lament (New York Ace 2004), ISBN 0441011632
Hex and the City (New York Ace 2005), ISBN 0441012612
Paths not Taken (New York Ace September 2005), ISBN 0441013198
Sharper than a Serpent's Tooth (Ace February 28, 2006), ISBN 0441013872
The Nightside series features the saga of John Taylor, a private detective. He is from a magical creation called "The Nightside", hidden deep in the tainted core of London's heart where it is always 3 A.M. People (and other things) come from all kinds of worlds (including fictional ones) and times to indulge in the secret and oftentimes perverse pleasures they can never pursue in their own worlds; and anything and everything is possible - the sight of a fallen angel burning eternally in a blood-sealed circle qualifies as a mundane sight. Native Nightsiders often possess a gift of some sort - often times a deadly one.
John Taylor is a 'finder.' If you pay him enough he can find anything, whether you want him to or not. At the time of the series opening, Taylor has refused to enter The Nightside for the past five years, fearful of a heritage that has made him one of the most feared and hunted men in a place where everyone has a price and an agenda. John has a reputation of being a hard and dangerous man among the denizens of The Nightside.
Taylor's gift can be deadly, and he is soon given the opportunity to prove that five years away have not lessened his powers. The secret of Taylor's childhood and mysterious destiny are fleshed out as the story progresses, but the one thing Taylor has been unable to find is the meaning and significance obviously attached to his life - although he's pretty sure it has something to do with his non-human mother who disappeared after he was born. Some unknown but very powerful someone (or something) has been trying to kill him ever since he was a kid, and the blank-faced, pseudo-beings called The Harrowing soon appear to claim their long-stalked prey and continue to appear through out the series. The very future of the Nightside is tied to John's search for the meaning to his existence
Combining the strength of film noir with utterly outrageous fantasy characters lends true stength to the series.