A mouse is annoying the family of Mr. and Mrs. Evil J. Evil, the scientists, and Snagglepuss is offered food and lodging if he will get rid of the pest. The trouble is that the Evil's little boy has been experimenting with the mouse, and the furry rodent is now six feet tall!

On the outskirts of town, the hard-nosed Vienna owns a saloon frequented by the undesirables of the region, including Dancin’ Kid and his gang. Another patron of Vienna’s establishment is Johnny Guitar, a former gunslinger and her lover. When a heist is pulled in town that results in a man’s death, Emma Small, Vienna’s rival, rallies the townsfolk to take revenge on Vienna’s saloon – even without proof of her wrongdoing.