Minions of the Moon

British Fantasy Society: Best Novel nominee (1999).

Kevin Grierson has a Shadow with a mind of its own. It likes thrills, it likes power, it likes the rush of drugs and danger. From the suburbs of Boston to the streets of New York, from the false glamour of advertising to the dark glamour of hustling and drug-dealing. Grierson's Shadow keeps him walking the edge of destruction and madness. Then a simple robbery goes horribly wrong. With the help of a flawed saint named Leo Dunn, Grierson struggles to banish his Shadow, and succeeds. Temporarily. Years later, sober and settled, at peace with his world, Kevin Grierson meets his Shadow again. And this time it won't go away.