Mirage

Ocean-dwelling Kampii Aluna and Hoku find themselves in the desert, a dangerous place for Aluna who is secretly growing her tail. They must race to the city of Mirage to warn the horselike Equians about the maniacal Karl Strand, who plans to conquer the Above World. With Strand's clone, Scorch, already there, the Equian leader vows to join Strand's army, threatening any who refuse. Aluna and her friends must win the desert-wide Thunder Trials to defeat Scorch and save the Above World from falling to Karl Strand forever.