As a mutated, three-headed, great white shark eats its way from one end of the ship to the next, the passengers have to fight the deadly predator using anything they can find.

In search of a new energy source, Russia accidentally reawakens the Kolossus – a giant robot doomsday device from the Cold War. At the same time, a new Mega Shark appears, threatening global security.

Survivors escape to a deserted atoll, after their boat during a Semester at Sea ship is sunk by a mutated two-headed shark. But when the atoll starts flooding, no one is safe from the double jaws of the monster.