Talise knows more about the ocean than any kid in Topsea. Any adult, too. As the best-and only-bathymetrist in Topsea, Talise is able to predict important things about the sea, like the next tide (Severely Low with a threat of Wildcard) or the arrival of Seaweed Season. What she can't predict, however, are her classmates' behaviors. Sometimes it's as if they're speaking different languages.

When Talise discovers a mysterious message in a bottle, her classmates believe it must have been sent by someone stranded on a deserted island. (Not to be confused with a dessert island.) But Talise is convinced the message is meant for her. And it's telling her to build a boat.

Everyone seems to think Talise is just being silly. Even Talise isn't exactly sure why she has to build the boat. And who keeps sending those strange bottled messages, anyway? All Talise knows is that she'd better finish building her boat fast, because an Extremely High Tide is coming?