Aria thought her life would go back to normal when she left her nainai's boba shop-and the monster living below it-behind in San Francisco. But while Aria and Nainai may have stopped the Big One, the aftershocks from her summer adventure are far from over. Each night, the monster visits Aria's dreams, calling her back to the caves below the city. Stranger still, Aria's discovered a newfound ability to manipulate water... but her powers aren't quite under her control. So Aria convinces her parents she needs another visit with Nainai, and she packs her bags and heads back to San Francisco. Beneath the boba shop, Aria and Nainai learn the monster's secret-he needs their help to return home. Can Aria learn how to harness her new powers (and a whole lot of boba) to bring the monster back to the sea, or will it be trapped under the city forever?