Deep in the rural swamps of Texas the mad Dr. Simond Trent is conducting experiments on the local swamp people in an attempt to discover the secret of evolution. When a party of oil surveyors comes upon his isolated laboratory he decides to take the final step and turn one of them into a grotesque amphibious creature.

A search and recovery team heads into the haunted swamp to pick up the pieces and Marybeth learns the secret to ending the voodoo curse that has left Victor Crowley haunting and terrorizing Honey Island Swamp for decades.

Bywater's native Seminole Indians believe the swamp will be bloodily revenged by its guardian spirit, a 'dark warrior', for its 'rape' by Frederic and son Jake Schist's oil-drilling, sold out by their own late chief Ted Sallis. The rig is illegally protested against by hot-head ecologists, who get blamed for vandalism on the site. New, outsider sheriff Kyle Williams suspects immediately local adolescent Billy James wasn't eaten during love-making there by a cayman but by a mysterious monster, which already made and soon makes new bloody victims in weird, inconsistent ways. Several people add to the danger.

Terror strikes when a swarm of Snakehead fish invade the Louisiana swamp land.