Darren Shan's "Procession of the Dead" is the first book in his "The City" series, which has been published in Britain in 1999. The next two books, "Hell's Horizon" and "City of the Snakes," are due to be published in the U.S. next year.
The main character, Capac Raimi, is one of the most compelling I've read. He does some of the most despicable, awful things between doing some of the most honorable, heartwarming things. It's an immersing read.