Crystal Doors — Kevin J. Anderson; Rebecca Moesta

Fourteen-year-old cousins Gwen and Vic have lived together ever since the mysterious deaths of Gwen's parents and disappearance of Vic's mother--until Vic's father accidentally transports them through a magical doorway to the island of Elantya. Vic and Gwen are soon caught in a tempest of ancient magic, vicious creatures, and fierce battles--all connected to a territorial feud with the sea-dwelling merlons, an age-old conflict between the bright and dark sages...and the cousins' own mysterious roots.