Simon R. Green's Nightside series is one of the more recent entries into the sf/fantasy mystery genre. Joining the ranks of Glen Cook's Garrett, Laurell K. Hamilton's Anita Blake and Jm Butcher's Dresden Files just to name a few. Green's approach to the genre is more in line with Cook's, a classic hard boiled detective mixed with a twisted sense of humor and good dose of parody.
Somewhere near London exists the Nightside. The place where all those things that we don't admit to existing polite society hang out and where all your dreams can become reality. Whether you like it or not. John Taylor is a detective and just his name can be enough to scare most the locals into giving him what he wants. Taylor's gift is to be able to find things. He can find anything he sets his mind too, but using his gift can have a price. Everything in Nightside has a price.
Though each book is a self contained with it's own resolution at the end, the series itself follows Taylor's quest to find out who he is, where he comes from and who really controls the Nightside. Taylor embarks on his adventures with a number of various companions, side kicks and enemies from all walks of life, death and miscellaneous realities. Green's back ground in Space Operas (the Deathstalker series) can be seen here in the unique characters he brings to his work.
The Nightside series is probably Green's best work to date. Good plots, interesting characters who, unlike many of the more one dimensional arch types often found in this style, go through some character growth and display occasional bits of of depth. All in all they are good fun and enjoyable reads.