Nani has discovered who she really is: the sole survivor of the imperial B'nli family. Though reluctant to claim her family title, Nani must do so if she intends to restore the broken Pillars of Milana. Nani, Tai, and their friends set sail into an oceanic Province, where they soon learn that even the watery borders of Bayrudaal cannot keep out their enemies. They must travel underwater and face the creatures of the deep, but the greatest danger of all is the Pillar they seek.