Despite the risks of visiting the hidden world, sixteen-year-old Rio Kaiser decides to help the people of Hyden, Rhyllia's last city, resist the Emperor and his army. Her rebellion against Hyden's military council puts Rio and her family in the center of a bitter dispute among the Hydeners and between the city and the Emperor. Making new bonds with Rhyllia's humans and creatures help her efforts, but the coming battles may still be too difficult for Rio to survive as her special abilities create additional problems for her to overcome.