Before you start reading, take a glance at the opening spread. You see a boy's bookshelf, with titles such as "Fairy Tales From a Forgotten Island" and "Joust Joking!".
You're about to read from each of these books. In order.
See, Charlie sat down to read his faaaaaavorite book, about a pirate. And the pirate in his story starts reading a book about the three bears... who notice that Goldilocks stole their favorite storybook... in which a knight reads from his favorite joke book... and on it goes until it comes full circle with the ghost in the scary stories book settling down to read HER favorite book about a boy called Charlie.
Every time you see a new book the font changes, you can see the dog-earred pages, there are little appropriate in-jokes - it's really very well done. It's a great concept, I think, and it's fun and fast to read.