Book one of Last of the Shardyn
Montana police chief Skip Walkins is hot on the trail of a murder suspect when he witnesses a drifter free the Lord of the Underworld. Seventeen years ago, five knights from Earth's magical twin, Theia, entombed Asmodeous the Pale, Lord of the Drynn, in Skip's town. Now that the dark god is free again, he's anxious to get back home and finish the war he began to enslave all life. It begins with killing the knights who trapped him.
Deprived of their magic, the knights fight back using whatever they can get their hands on, from samurai swords to assault rifles. Skip gets reluctantly drawn in to their struggle while Donovan Smith, the demi-god murderer whom Skip was after in the first place, plots to find the Lord of the Underworld and butcher him on his own.
Together, these unlikely heroes might just save the world. If they don't kill each other first.