Stormchaser: The Edge Chronicles, Book 5

Since his childhood in the Deepwoods, young Twig has always longed to soar above the forest canopy and explore the sky. Now a lowly crew member on his father's sky pirate ship, the Stormchaser, his dream seems fulfilled. But a much higher destiny awaits Twig as plots and treacheries from many years ago bring the lofty city of Sanctaphrax, home of the Edgeworld's most learned academics, to the point of disaster. For the city is built on a giant rock, floating high in the sky, its future balance dependent on stormphrax, a valuable yet extremely volatile substance obtained only from the heart of a Great Storm at the very instant it unleashes its most intense power. And only a ship such as the Stormchaser could risk entering the Storm.