A series of brutal attacks in the Louisiana swamps leave the local police mystified. Sending in a coroner originally from the area and a biologist to investigate, they learn that a group of genetically engineered Chinese snakeheads are responsible. The fish chase the investigators upstream, where the fish trap them on a houseboat with several other locals. Meanwhile, a group of big-game hunters track down the fish. It all boils down to a fight for survival with the voracious predators slowly picking off the humans.