A community of mice and birds are living and playing peacefully until the arrival of the title character: a mechanical cat who wants to eat so he picks a bird to take to his castle. All of the birds friends follow the victim there but many are given electrical shocks when they confront the cat. A mouse who lives in a supermarket hears a distress signal on his radio and, after eating Limburger cheese, turns himself into the costumed superhero Mighty Mouse (though he was known as Super Mouse at the time). As he flies to the castle, Mighty fights and defeats the mechanical cat as the head falls off and the bird escapes making possible another happy ending.