The KnightStick Chronicles, Rough Justice

Justice is real... and he is a dick. After the death of his partner, John Morgan resigned himself to a life at the bottom of a bottle. But fate, and something much stranger, had other plans. A chance encounter forces John out of his reverie, and into the service of a spirit of justice. He is bestowed a mysterious talisman, thrusting him into a world of nightmares, and given a single choice; answer the prayers of the tormented innocent, or else be driven insane by visions of their suffering... Falling back on his old skills as a former cop, and donning the antique attire of lawmen of old, John must confront a new world of evil and corruption. Will he be able to rise to the challenge? Or will his past trauma prove more formidable than an army of shadow monsters...