Billy and his sister Sheena are spending their vacation on a tiny Caribbean island with their Uncle Dr. Deep. The sparkling blue waters are the perfect place to go snorkeling and exploring. Billy is ready for a massive underwater adventure, even though he has been strictly warned to stay away from the beautiful coral reefs. Unable to resist the peaceful, crystal-clear water, Billy dives in, only to discover that he is not swimming alone. There is something dark and scaly lurking far below the surface. You will feel your heart race as Billy comes face to face with a mysterious creature that is half-human and half-fish. Get ready to dive into a thrilling mystery as Billy uncovers a secret hidden deep in the ocean. He must use all of his courage to navigate the dangerous waters and figure out what the scaly creature truly wants.