The Edge of Worlds [Books of the Raksura 04] - Martha Wells

An expedition of groundlings from the Empire of Kish have traveled through the Three Worlds to the Indigo Cloud court of the Raksura, shape-shifting creatures of flight that live in large family groups. The groundlings have found a sealed ancient city at the edge of the shallow seas, near the deeps of the impassable Ocean. They believe it to be the last home of their ancestors and ask for help getting inside. But the Raksura fear it was built by their own distant ancestors, the Forerunners, and