Memoranda and The Great Raven, so it could hardly fail, but trust me, it was pure delight. One part police/crime mystery, one part Neil Gaiman, with a good sprinkle of history and geography, a dollop of gore, a generous serving of laughs... This book has it all.
Peter Grant is a London police constable who becomes an apprentice wizard, working for the mysterious and older-than-he-seems Detective Inspector Thomas Nightngale, dealing with a supernatural serial killer, ghosts, and a territorial dispute between Mother Thames and Father Thames, among other things. The son of a white jazz musician and a woman from Sierra Leone, Peter is also clearly a geek who recognises an Edwardian smoking jacket from watching Dr Who. (This is not altogether surprising as Ben Aaronovitch has actually written for the show.)
The good news is that, having raced through the first book in the series at top speed, I know that several more volumes await. I actually walked to the Northcote library to grab the next two while they were still on the shelf. But after that I might be in trouble -- my New Year's resolution is to not buy any more books till I finish the ones I've already got... But I can foresee a serious Peter Grant addiction coming on, in whose grip I will be helpless.