Manhattan Dying — Michael C. Madden

Samuel Austin Martin, a struggling author from Melbourne Australia, is on a trip to New York to promote his new book when Earth is invaded by an agressive, supernatural world. With all modern technology rendered totally useless, Sam must fight demons, monsters, dragons and massive, medieval armies to get home. His impossible plan: get out of New York, cross the USA, find a way home without getting caught up in the ever growing war. Events conspire to draw Sam deeper and deeper into becoming a pivotal figure in the struggle to save Earth from the horrors that are befalling it.