Crystal Doors Omnibus : The Complete Trilogy in One Volume: Island Realm, Ocean Realm, Sky Realm

Fourteen-year-old cousins Gwen and Vic are transported through a magical doorway to the island of Elantya, where they are caught in a tempest of ancient magic and fierce battles. Unable to get home, they study magic and science in elantya, and form friendships with other students. Thrust into the middle of an age-old conflict between bright and dark sages, the cousins begin to discover their own mysterious roots. Gwen and Vic and their friends defend the worlds beyond the crystal doors in battles against the dark sage Azric. In battle, the companions face Azric by land and sea, and then take to the skies in a showdown with the evil wizard and his dark forces.