In the fog-laden hills of San Francisco sits a sleepy independent boba café. Run by Jing Li and guarded by her kitty, Bao, it comfortably fades into the background. But inside the boba café, there's a secret. Jing is the keeper of the monster of San Francisco. Each day she prepares one giant boba for nine hours to feed it.

When Jing's granddaughter, Aria, comes to stay with her for the summer, she makes it her mission to turn the café around. Aria is quickly aided by Bao, who gives birth to eight perfect kittens. Aria spreads the news of the boba cat café on social media and overnight it is overrun with excited customers. Each day Nainai Li (Grandma Li) finds reasons to close the café, but the demand only increases.

When she opens, the hill monster is left hungry and small earthquakes begin to plague the city. When Aria secretly follows her nainai to the hill monster's cave, she isn't sure what awaits. Will Aria be able to reason with the monster, or will she become its new favorite meal? Or might she disturb its underground existence and cause the Big One?