Melvin White, a neurotic, accident-prone cop who gets demoted to the night shift, secretly moonlights as the Unknown Comic, an anonymous stand-up comedian who performs with a paper bag over his head. When someone using the same guise commits a string of bar robberies in town, some begin to suspect that White is the culprit.

爱达荷州一个小镇的有毒垃圾倾倒使一个小男孩变成了可怕的变种怪物。镇上的警察局长和一个政府科学家联手阻止了这个怪物，这个怪物很快就杀死了镇上的市民。