On an idyllic summer's day, the peace is suddenly shattered as beachgoers in the water start screaming and convulsing. When rescuers finally get to them, some are in agonizing pain while others are already dead. Something deadly is hiding in the warm waters of Pompano Beach, Florida and it is up to a hastily gathered group of scientists to find out what it is. When they start investigating, they realize that this is only the beginning of the terror that threatens not only beachgoers but anyone in the waters around Florida's east coast. Whatever it is, it is spreading northward threatening the entire eastern seaboard of the United States. The scientists must quickly determine what this terrifying threat is and to stop its catastrophic killing spree before it is too late.