Dominion

A hitman and his paranormal companions are all that stands between London and a demon on the warpath in this urban fantasy novel with gangster movie flair
 
In the tunnels deep under London, the Earth Elementals are dying.

Hunted by something they know only as the Rotman, the Elementals have no one trustworthy they can turn to. Enter Don Drake, diabolist and semi-reformed hitman, and an almost-fallen angel called Trixie.

When the matriarch tells Don that Rotman is actually the Archdemon Bianakith, he knows this is going to be a tough job. Bianakith is the foretold spirit of disease and decay whose aura corrupts everything it comes near, and even the ancient foundations of London will crumble eventually. Now Don, Trixie and the Burned Man must hatch a plan to keep Bianakith from wiping out the Elementals and bringing down the city.

But the Burned Man has other plans—and they may have dire consequences for everyone.