Charged with discovering the owner of a fish-shape glass bottle, Herbie Lemon and his friend Vi discover that it is tied to the ocean creature Garganits, a monster with the ability to generate powerful storms. But others in the town of Eerie-on-Sea also lay claim to the bottle, including beachcomber Mrs. Fossil who found it, museum director Dr. Thalassi, and local fishermen. Herbie and Vi must discover if the bottle belongs to Garganits, and if so, who stole the precious artifact from the monster.