Young sisters Kate and Lisa travel to Mexico for a vacation filled with sun, fun and adventure. But Lisa needs some extra persuasion when Kate suggests that they go diving in shark-infested waters. Safe in their protective cage, the thrill-seeking siblings come face-to-face with a group of majestic great whites. Their worst fears soon become a reality when the cage breaks away from their boat, sending them plummeting to the ocean floor with a dwindling supply of oxygen.