What does Big Red Book represent?

Billy’s big red book is a symbol of adventure. Billy has read the book Professor Abacus Abernathe’s Compendium of Heroes, Adventurers, and Other Intrepid Travelers multiple times before he even starts his own adventure. As he rides along with his brother, Billy uses the book as a reference for the way he should behave. For instance, when Emmett tries to go to Woolly’s family’s summer camp alone, Billy refers to the story of Xenos and believes he should go along with Emmett in case he is needed. Xenos was a character who often did not make a big impression on the reader, but who was the one who would save the hero at the last moment. When Billy does begin writing his own story of adventure, as the author suggests that he does, Billy writes not his story, but Emmett’s.