Empires of Flux & Anchor (Soul Rider, Bk. 2)

Cassie did not feel the soul rider enter her body... but suddenly she knew that Anchor was corrupt, and that, far from being a formless void from which could issue ony mutant changelings and evil wizards, Flux was the soure of Anchor's very existence. The price of her new knowledge is exile, yet Cassie and the Rider of her soul are the only hope for the redemption of both Flux and Anchor.