Rivers of London by Ben Aaronovitch

Probationary Police Officer Peter Grant is doing sentry duty in Covent Garden in the aftermath of a body being found missing its head when he spots a possible witness, but as the short pale faced man steps into the light identifying himself as Nicolas Wallpenny it becomes clear that he is, in fact, transparent. Well trained PC that Grant is he continues with the interview and it becomes clear that Wallpenny's information is credible. Grant only speaks of his experience to fellow probationer (and unfulfilled love interest) Lesley May, but goes looking for Wallpenny for more information and it's then that he is asked what he's doing by Detective Chief Inspector Thomas Nightingale who responds to Grant's honest reply that he's looking for a ghost with interest. Nightingale turns out to head up a division of the Met that deals with the supernatural, but the joy of this book is that Grant is never more than a good well trained police officer so there is a strong thread of self deprecating humour throughout. The ideas are fascinating, a murderous spirit and personfications of the buried rivers of London, turf wars on a supernatural scale. There are similarities to writers such as Mieville and JK Rowling, tv staples such as X Files, Torchwood and Doctor Who, to Hot Fuzz and the graphic novel character Constantine but Aaronvitch writes about it all in a completely fresh way creating a world that whilst fantastical is still completely consonant with present day London and all its horrors, grime, wonder and human character.