Thrilling and terrifying, this adventurous tale opens with a group of wakeboarders being attacked and devoured by a two-headed great white shark. Meanwhile, Sea King, a Semester at Sea ship led by Professor Franklin Babish (O'Connell) and his wife, Anne (Electra), hits a dead shark.
The shark becomes lodged in the boat’s propeller, damaging the ship's hull and causing the boat to take on water. Soon after, the two-headed shark attacks the boat and breaks the radio antenna, preventing ship co-captain Laura (Thompson) from summoning help.
Professor Babish and the students use a dinghy to take shelter on a nearby deserted atoll, while Anne remains on the Sea King with Laura and the ship's crew, Han (Webb) and Dikilla (Valentin). Laura enters the water to repair the ship's hull, and is quickly ripped apart by the two-headed shark.
Meanwhile, professor and the students explore the atoll. Assembling in an abandoned fishing village, they set out to search the atoll for scrap metal to help repair the boat. Haley (Jackson) and Alison (English) decide to go swimming topless with Kirk (Conner), only to be attacked and eaten by the two-headed shark.
The rest of the group meet up and find two small speedboats before an earthquake hits, causing Professor Babish to fall and badly injure his leg. Dana (Bach) bandages Babish's leg with her shirt, while Jeff (Carmouze) and Mike (King Leslie) accompany him back to the Sea King on the dinghy. On the way back, Jeff and Mike discover Laura's severed hand in the water. They are attacked by the shark and eaten while attempting to swim back to the Sea King.
The students find two boats on the island, which Kate (Hogan) and Paul (Gallegos) manage to fix. Cole (Ward) finds a gasoline tank to fuel them, but then steals one together with Ryan (Charles), Jamie (Vera) and Alex (James). Kate, Paul and Dana follow them in the other boat.
They are all unaware of the shark, which attacks Cole's boat. Ryan falls into the water and is eaten, alerting the others to the shark's presence. Paul concludes the shark is drawn to Cole's boat as it has a bigger engine. Cole also deduces this and bails; the shark eats Jamie and Alex. When the survivors reach shore, Kate furiously confronts Cole for his actions. A few minutes later, the Sea King is abandoned and the survivors meet on the island.
Shortly afterward, another earthquake hits. The group realizes that the earthquakes are actually caused by the atoll collapsing in on itself. Escape being ever more urgent, the group hooks up a generator to metal poles and places them in the water to distract the shark with electricity while Kate and Cole travel to the Sea King and repair the hull.
The plan works until the shark attacks the poles, knocking Han and Dikilla into the water to their death. Kate fixes the ship, only for Cole to drive away without her, forcing her to swim back to the atoll. The two-headed shark attacks the Sea King, causing it to sink and send out a distress signal; Cole is eaten trying to escape on a lifeboat. The atoll is sinking too, prompting everyone to flee for their lives. Many of the group end up in or near the water as a small tsunami hits the island, losing their lives to the shark's appetite.
The only survivors are Kate, Paul and Kirsten (Nobili), who had taken shelter in a village chapel and escaped the shark when it broke in. They discover a gasoline tank, and lure the shark towards it. Kate plans to stab the shark and is nearly eaten, but Kirsten sacrifices herself to try to blow up the shark as it eats her.
However, only one of the shark's heads get blown off. Kate and Paul find one of the boats and turn it on as a decoy, taking shelter on part of the remaining atoll. The shark attacks the unmanned boat. It bites the motor, which explodes, finally killing the shark (a homage to Jaws). A helicopter arrives, saving Kate and Paul, leaving only 2 survivors out of 23 people.
