Huckleberry Finn is a boy who has been taken away from his abusive father, and has been adopted by the Widow Douglas and her sister, Miss Watson. His father, "Pap," has disappeared, although Huck thinks he will return, seeing as how Huck has recently come into a great amount of money (his share of the treasure from the end of The Adventures of Tom Sawyer). While Huck likes living with the widow better than his father, he feels trapped, as the widow attempts to "sivilize" him and teach him religion. Huck finds her ways confining. To keep his sense of freedom, he sneaks out at night to meet Tom Sawyer. Tom and Huck meet up with other boys to form a gang. They participate in some "adventures", but Huck gets bored with these quickly. Pap shows up again, and Huck bequeaths his fortune to Judge Thatcher, knowing his father will try to steal it. Angry at this turn of events, Pap kidnaps Huck. Huck manages to eventually escape by faking his own death. He builds camp on Jackson's Island.
On the island, Huck is free once again. However, he soon discovers he is not alone. Miss Watson's slave Jim has run away because she threatened to sell him down the river. Huck is uncomfortable with the runaway slave, but they build a fast friendship. Having found a house with some extra clothes, Huck dresses like a girl and goes ashore to get some information. He finds out that Jim is wanted and they must leave the island. He and Jim set out on the river on a raft, sleeping by day and drifting by night. Living this way, they get to know each other, and Jim tells Huck about his children. Huck slowly comes to realize that Jim is a human being, just like anyone else. This knowledge goes against everything he has been taught, living in the virulent racism of the South.
Huck and Jim plan to drift down to Cairo, Illinois, where Jim can escape to the North to be free. But, a steamboat crashes into their raft and separates them. Huck swims ashore and is taken in by the Grangerford family, who are fighting a feud with another local family, the Shepherdsons. He lives with the Grangerfords, making friends with their son Buck. Buck soon dies in a fresh bout of feud violence, and Huck reunites with Jim, floating once again down the river. Huck and Jim rescue two criminals, who identify themselves as a duke and a king. They take the best sleeping places on the raft and the best food, expecting Jim and Huck to wait on them. They employ different schemes to make money along the river. They attend a religious camp-meeting, and the king takes up a collection for himself. They stage a Shakespearean show in a town where Huck witnesses a street shooting and lynch mob, but the show is a huge flop. So they produce another show, which involves nudity and vulgarity, conning the townspeople out of their money.