The New Deadwardians — Dan Abnett

In post-Victorian England, nearly everyone of the upper classes has voluntarily become a vampire in order to escape the lower classes who are all zombies. Into this simmering cauldron is thrust Chief Inspector George Suttle, a lonely detective who's got the slowest beat in London: investigating murders in a world where everyone is already dead! When the body of a young aristocrat washes up on the banks of the Thames, Suttle's quest for the truth will take him from the darkest sewers to the gleaming halls of power, and reveal the rotten heart at the center of this strange world.