The Haunting of Alaizabel Cray, by Chris Wooding.
Thaniel is a wych-hunter in a dark, damaged version of London which is overrun with creatures that haunt, maim and kill. The town is not only haunted by night-ghasts, but also by a semi-legendary Fraternity, rumored to have control of all the city’s operations, and rumored to be a conduit for powers even more destructive than those the city has already seen. As those powers intensify to the point of spiraling out of control, Thaniel is drawn to a showdown which could destroy his world and all he loves.
Whether he succeeds, and whether he is able to save the world he is sworn to protect, remains to be seen.