Herman, the city-slicker mouse (looking like a cross between James Cagney and Lee Tracy) visits his barn-mice cousins in the country. There he sees that the barn also has a cat, and Katnip the Kat, is one mean dude who has put most of Herman's relatives on crutches and in slings, and even dispatched a couple of them to Mice Heaven. It is up to city-wise Herman to outwit the country-wise cat but the country cat has been to a couple of County Fairs himself, and proves to be nearly more than Herman can handle.