When a greedy oil baron sets his sights on drilling in a Louisiana swamp, a monstrous creature is awakened. The baron and his associates are killed in the swamp thicket, spurring an investigation led by Sheriff Kyle Williams. Although the Seminoles are initially suspected of the murders, the swamp creature, known as Man-Thing, is the killer. A gruesome creature made of plants and vines, Man-Thing possesses strange and dangerous powers.