Mr. Junkett (Sherman Hemsley), a vehicle maintenance inspector, was so displeased when he inspected the Magic School Bus that he decides to take it to the junkyard to crush it. The Friz and the class have to do something to save their bus. Naturally, they have decided to shrink and go inside it. All the problems seem to be caused by peanut butter, as Mr. Junkett was eating a peanut butter sandwich while he was inspecting the bus.