Hell's Horizon — Darren Shan

In the City, The Cardinal rules, and Al Jeery is a loyal member of his personal guard. But when Al is pulled from his duties at Party Central to investigate a murder, an unexpected discovery leads him in a new direction, where his loyalties and beliefs will be severely tested.

Soon he is involved in a terrifying mystery that draws in the dead, the City's Incan forefathers, the imposing figure of The Cardinal, and the near-mythical assassin Paucar Wami.

Wami is a law unto himself, a shadowy, enigmatic figure who can apparently kill anyone he chooses without fear of punishment or retribution. And Al is about to find out that he has a lot more in common with Wami than he could ever have imagined...