When Mike Mulligan and his steam shovel, Mary Ann, lose their jobs to the gasoline, electric, and diesel motor shovels, they go to a little country town where they find that one new job leads to another. On board pages.
Katy, a brave and untiring tractor, who pushes a bulldozer in the summer and a snowplow in the winter, makes it possible for the townspeople to do their jobs.
Maybelle loves to carry people up and down the hilly streets of San Francisco, until the City Fathers decide that she should be taken out of service in the name of progress.