Just finished reading:
"Whispers Under Ground" by Ben Aaronovoitch (just published last month).
http://www.the-folly.com/books/rivers-of-london-uk/
Its a pulp. (ie, won't change your life in any way) but its fun.
Third in a series, "Rivers of London".
Echoes of Charles Stross and Jasper Fforde.
Even better if you're familiar with (London) NW5, WC1, SW2, SW9.