A series of brutal attacks in the Louisiana swamps leave the local police mystified. Sending in a medical investigator, Sam Rivers , discover that a group of genetically engineered Chinese snakeheads are responsible. The predator fish chase the investigators up the river, where a team of others is already trapped. Meanwhile, a group of big-game hunters track down the fish. It all boils down to a fight for survival with the voracious attack fish slowly killing off the humans.