A bunch of mice are living in a shack, where their friend, a dog, brings them food and protects them from a clowder of cats. However, when the cats seize the dog, stick him in a crate and put it on a railroad track where a train is about to smash everything, in comes MIGHTY MOUSE.
Mighty Mouse, Paul Terry's most successful series, was aimed squarely at very young children who could imagine themselves as tiny mice, with a Superman figure to protect them. Any interest I might have in the series was worn out long ago, because they soon settled into the same plot line: mice are threatened by cats, Mighty Mouse beats up the cats, mice jump and cheer. There are a couple of good gags early on in this particular short -- I like the one about the keyhole -- and Terry maintained a level of competence throughout his forty-year career as a cartoon producer, but this is much of a muchness and as forgettable as almost all of the Mighty Mouse cartoons are.