Kai and Kishi share the same futon, the same face, and the same talent for pearl diving. But Kishi is the obedient daughter, while Kai tries to push boundaries, and sometimes they fight as fiercely as only the closest of twin sisters can. Still, when Kishi is stolen by the legendary ghost whale, nothing will stop Kai from searching deep in the ocean to bring her home. But such a rescue is beyond the power of an ordinary mortal. Kai strikes a deal with the gods: shell steal a magic pearl from faraway Sky Mountain in exchange for her sisters soul. Kai must navigate encounters with scheming bandits, a power-hungry warlord, and a legion of conniving fox spirits, all the while keeping to her mission to save her sister. And when a new friendship becomes something almost as powerful as her love for her twin, Kai must make impossible choices and risk everything just to get home again.