On the verge of a breakthrough in his quest to wipe out world hunger, altruistic botanist Dr. Alec Holland (Ray Wise) is placed under the protection of special government agent Alice Cable (Adrienne Barbeau). Mad outlaw scientist Anton Arcane (Louis Jourdan) wants to steal Holland's research for his own nefarious ends, but an unforeseen accident during the heist turns Holland into the Swamp Thing, an enormous plant-like creature that fights back against Arcane's henchmen to save Cable.