Grimoire of Stone — Keith Harvey

A hundred years after a World War, Moses Stern, spy and gunslinger, serves the Vatican in La Ciudad, Mexico. On a mission north of the Rio Concho, he falls prey to vampire witches and Coyote, a shape-shifting trickster. The witches are searching for a human champion to rid the earth of dragons; and, when they capture Stern, they realize they have found their man. All they have to do is persuade him to travel to the dragons' realm, discover why they have come to earth, and figure out a way to send them home. He agrees. But, once there, he finds four elemental realms in turmoil, beset by tyrant kings and terrible demons. He also learns that returning home may be nigh impossible. So, when a demon offers him unlimited power and a way back, he makes a Faustian bargain. Earth and Stern will never be the same again.