The bookstore/ wagon is named "Parnassus On Wheels" (hence the title), and naturally, it's name is inspired by literature. Parnassus is a mountain in Greece near Delphi. In mythology, this mountain was the home of the Muses, who were the goddesses of science, literature, and the arts.
In short, this is a quick, fun story, and a celebration of the power and importance- and joy- of books.