The Verdant Passage: Dungeons & Dragons: Dark Sun: Prism Pentad, Book 1 (Unabridged‪)‬

Under a previous sun, Athas teemed with life. The sorcerer-king, after obtaining immortality for himself, united all lands under the power of his magic. But power-hungry overlords have carved the lands into pieces - setting themselves up as sorcerer-kings--and survival depends on the optimism of three steadfast people.