When fisherman Chen Haisheng divided the family property, all he received was an old, leaky boat. Yet he brought home a mysterious girl named Xiaoman whom he found by the sea, who could understand the language of the ocean. Xiaoman accurately predicted a returning tidal bore, saving Chen Haisheng and Ergou. She then discovered a nautical chart of Blackstone Bay left behind by her father in a hidden compartment of the old boat. When the entire village rushed to the eastern tidal flats to catch crabs, Xiaoman insisted on taking Chen Haisheng to the unfrequented western mudflats, where they unexpectedly dug up a basket full of green crabs and a rare giant crab, selling them for a high price. His sister-in-law Wang Xiumei grew jealous and followed them, setting the stage for a story of oceanic secrets and family conflict.