The Legions of Fire: The Books of the Elements, Volume One

In this fantasy novel set in Carce, a world based on Europe during the later Roman Empire, four young people—Corylus, Varus, Hedia, and Alphena—must confront dangerous magic to prevent catastrophe. Far to the north, magicians perform a ritual on a volcanic island designed to open a gateway for supernatural creatures to devastate the planet and destroy all life. Unaware of this threat's source, the four protagonists separately investigate mysterious and ominous events occurring in Carce, the center of civilization. Through magical journeys into other realities where gods and fantastic creatures either aid or oppose them, each must succeed or face the world's destruction. The Legions of Fire is the first book in a fantasy quartet set in the world of Carce.