Blue Wing lives with her guardian Siringen, a shark caller, on the outskirts of her village. She's desperate to become a shark caller herself to avenge the death of her parents, who were killed by a notorious shark, Xok. But it's against tradition for a girl to become one, and Siringen believes Blue Wing still harbours too much anger in her heart. When American professor Atlas Hamelin and his daughter Maple arrive on the island, Blue Wing is charged with looking after the infuriating Maple. But, slowly, Blue Wing finds that Maple might be the one person who can understand her. And when they discover that Professor Hamelin is secretly searching for an ancient treasure, they find themselves on a journey to depths of the ocean, where Xok lies waiting...