The bus is acting up, so Ms. Frizzle decides to take it to the Body Shop for repairs, owned by R.U. Humerus (Tony Randall). Meanwhile, Ralphie has been dreaming what it would be like if he had a robot to do all his chores. So he and the rest of the class (minus Keesha) want to try building one using all the gadgets in the body shop. First, though, they will have to understand how bones and muscles work.