Bargain @ $1.99 from Ace Books in Canada & US (Orbit has the UK rights, IIRC; should be the same price at all the usual retailers):
The Rhesus Chart by Charles Stross (
Wikipedia), 5th novel in his Hugo Award-nominated Laundry Files series of supernatural urban fantasy centred around a secret government agency with decidedly Lovecraftian bureaucracy. These originally started out as spy thriller spoofs pastiching particular styles of classic espionage novels for the first 4, but this one shifts the tone to exploring urban fantasy tropes (this is the vampires one) and is a decent jumping-on point if you haven't read the rest (#1 was also on sale a while back) with a reasonably standalone, self-contained story (start of a new overarching plot arc which continues through the next few books).
The Hugo Award-winning author of The Delirium Brief reveals the secrets of The Laundry Files in an adventure of Lovecraftian horror and espionage hi-jinks...
As a newly appointed junior manager within the Laundry—the clandestine organization responsible for protecting Britain against supernatural threats—Bob Howard is expected to show some initiative to help the agency battle the forces of darkness. But shining a light on what’s best left in the shadows is the last thing Bob wants to do—especially when those shadows hide an occult parasite spreading a deadly virus.