The Serpent Sea: Volume Two of the Books of the Raksura

Moon, once a solitary wanderer, has become consort to Jade, sister queen of the Indigo Cloud court. Together, they travel with their people on a pair of flying ships in hopes of finding a new home for their colony. Moon finally feels like he's found a tribe where he belongs. But when the travelers reach the ancestral home of Indigo Cloud, shrouded within the trunk of a mountain-sized tree, they discover a blight infecting its core.