Worldbinder: The Sixth Book of the Runelords : After the events of Sons of the Oak, Fallion and Jaz, the sons of the great Earth King Gaborn, are living as fugitives in their own kingdom, newly invaded and secretly controlled by supernatural being of ultimate evil. The sons are hiding until they can regain their rightful places in the land.
Fallion seems destined to heal the world, and feels the supernatural calling to act. When he calls on his powers to do so though, two entire worlds collapse into one, and every living thing on both worlds is transformed into an entirely new being—yet still somehow the same. Evil is certainly still the same, and may have influenced this for a terrible purpose.