Twain does a good job in this novel of integrating the exposition and back story smoothly. He includes literal back story in the preface, when he tells the readers where the story came from. After that, though, most of the exposition is slipped into the story more smoothly. For example, look at Aunt Polly's longish speech at the start of Chapter 1. It works like a monologue in a play. Polly tells readers that Tom is her sister's son, that her sister is dead, what his character is like, that she has trouble punishing him, and so on.
what is the exposition or backround of the story, "the adventure of tom sawyer"?