Billy and his sister, Sheena, are visiting their uncle Dr. Deep on a tiny Caribbean island. It's the perfect place to go exploring underwater...and Billy's ready for an adventure. There's only one rule to remember : Stay away from the coral reefs. Still, the reefs are so beautiful. So peaceful. Billy can't resist. But he's not alone in the water. Something's lurking deep below the surface. Something dark and scaly. Something that's half-human, half-fish.

Robert Lawrence Stine (born October 8, 1943), known as R. L. Stine and Jovial Bob Stine, is an American writer. Stine, who is often called the "Stephen King of children's literature", is the author of dozens of horror fiction novels, including the books in the Goosebumps, Rotten School, Mostly Ghostly, The Nightmare Room and Fear Street series. Some of his lesser-known works include a Space Cadets trilogy, two Hark gamebooks, a two-part novel The Beast and dozens of joke books.