Out of the Darkness by Kaden Gardner

When a pair of United States Marshals trace two brutal killers to a small mining town in New Mexico, they find themselves drawn into the middle of what can only be described as a supernatural war where the fate of every living soul on the North American Continent rests in their hands. No one is who they seem. Their enemies are ancient, brutal, and cunning. They don’t die easily. Can Ken Sullivan and his mentor Roy Adkins use their wit and their guns to save lives? Or will they die horrible deaths?