Eleven year-old Connie lives a dreary life on the windswept shores of Cornwall. With her only company being a drunken father, overworked mother, and the mad Granny Florence, she finds solace at the top of the headland, looking over the sea. But one night, when she sneaks down to the nearby cove, she stumbles on a remarkable discovery.A young mermaid girl named Heloise - her half-sister.The two strike up an instant friendship, but storms are brewing on the horizon. Can their newfound bond survive?