Cartoon adventures of builder Bob and his friends - Travis the tractor, Scoop the bulldozer, Lofty the crane and Dizzy the cement mixer. Bob's Auntie Dora, a stickler for tidiness, is coming to stay. Bob asks the gang to tidy up the yard - while he goes to get his suit - and chaos ensues. However, help arrives in the shape of an old lady, whom the Machines assume to be Aunt Dora. Bob comes back to find the yard spick and span, but finds that the old lady isn't his aunt at all!