Crystal Doors 3 Sky Realm

After facing peril by land and sea in the magical world of Elantya, cousins Gwen and Vic take to the sky in the final book in this YA fantasy trilogy.

Following their adventures in the novels Island Realm and Sea Realm, fourteen-year-old cousin Gwen and Vic—together with their new friends—will now have to face their most challenging adventure yet. It is time to discover if they can forge the magical Ring of Might . . . and if it will be enough to challenge the dark sage Azric.
As next in line to the throne of Irrakesh, their friend Sharif will have to choose between duty and destiny. the sky city. But before he can, the flying city is taken hostage by Azric's monstrous winged army. Now Gwen, Vic, and their friends must engage in combat among the clouds in the final showdown with the evil wizard and all of his dark forces.