Poseidon's answer to Cerberus eats its way from one end of a cruise ship to the other.
The world's greatest killing machine is three times as deadly when a mutated shark originating from the Great Pacific garbage patch eats its way through an island research facility. As the survivors escape, the shark finds a party boat, forcing the passengers to fight the deadly predator using anything they can find. As the shark chomps its way from one end of the boat to the other, the survivors from the research facility arrive and attempt to help the passengers escape. But they very quickly discover three heads are much more difficult to kill than just one.