At the state-of-the-art Shining Sea Aquarium in Southern California, the remains of a sick dolphin infected with a novel virus are accidentally fed to the other marine animals, including mako sharks and a giant octopus! The virus has already caused extremely aggressive behavior and mutations in animals at other zoos, resulting in injuries and deaths. The infected marine creatures—octopuses, sharks, sea lions, giant crabs, a crocodile, a walrus with impressive tusks, and even starfish—now begin hunting down any humans and tormentors still inside the vast complex of underwater tunnels and aquarium tanks. Security officer Eddie "Clu" Cluwirth, along with institute scientist Dr. Karen James and medical assistant Miranda, are scrambling to save the humans and prevent the infected marine animals from escaping into the wild.