Charlie, who is nervous about his first day of school, and Dumpy the Dumptruck, who is nervous about his first construction job, gradually adjust to their new settings after making new friends.
When Mrs. Barnes declares that "It's Apple Day," Dumpy wants to help and finally gets his chance once all of the apples are picked and made into pies, apple butter, and candy apples.
After Charlie and his grandfather fix up a rusty old dump truck, they use Dumpy to help Trundle the tractor, Bee Bee the backhoe, and Stinky the garbage truck build a new barn.
A gang of mini mechanics introduces the tools and equipment needed to be a good mechanic, and describes six different diggers and dumpers, and how they are used.