After the captive great white shark dies, and a Sea World employee; Shelby Overman is found slain by a shark, Mike comes to a disturbing realization: the captive great white was a baby, and its monstrous 35-foot mother is somewhere in the park! Panic ensues, and the newest Bruce incarnation strikes again, nearly killing several people. Mike's dolphin-trainer girlfriend fears for the lives of her two young dolphins, Sandy and Cindy. Meanwhile, in the Undersea Kingdom, an enormous maze of underwater Plexiglases tunnels, an announcement is made to get back above the surface immediately; the monstrous mom could be anywhere in the park. Initially confused, the people in the Undersea Kingdom calmly follow their guide to the exit, until they catch a glimpse of the enormous great white shark! All heck breaks loose, as all in the glass tunnel struggle to escape; the only thing standing between them and the enormous shark is a thin layer of Plexiglases, but the shark is the least of their worries because if the glass is broken, water will leak into the tunnel and drown all those who aren't devoured by the beast. The shark smashes into the glass, and makes a large crack. Water spurts through the leak and begins to fill the tunnel. The terrified tourists find refuge in a water-tight room, but before it closes, they are already up to their waists in deadly-cold water. If they don't get out soon, they'll die in this watery tomb. A rescue mission begins, involving many close encounters with the shark. Feeling somewhat responsible; oceanic adventurer, Philip FitzRoyce decides to take on the shark by luring it into an enclosed pipe, using a lifeline to get one over momma shark. Unfortunately it breaks and on seeing his distraction, said shark suddenly rushes him and suddenly Philip finds himself struggling for his life inside the shark's massive jaws. Despite his efforts to blow her up, he is overwhelmed and chewed up. Thanks to the heroism of Sandy and Cindy the dolphins, the trapped tourists are saved, but the shark survives, and attacks Mike, his girlfriend, Calvin, and another man in the control room, smashing through the glass. Water fills the room. Calvin's nephew is devoured while Calvin escapes. Only Mike and his girlfriend remain. Despite being stuck our undaunted female shark goes Mike's girl, and as she does inside her mouth, Mike sees his last hope: Philip stuck in her jaws, still clutching his grenade with the pin still inside. Mike grabs a long pole, and after three tries, he pulls the pin from the grenade. Mike and his girlfriend swim for cover, seconds before the grenade explodes, blasting apart the beast and leaving nothing but blood and teeth behind. The two survivors swim to the surface and are happy to find that Sandy and Cindy survived.