Adventures of Huckleberry Finn, on the other hand, contains much less of the perpetual jokes and scrapes of the first book. Instead, Huck is faced with the emotional growing pains of becoming a man in a morally flawed society.
At the beginning of the novel, Huck lives with the Widow Douglas, who wants to "sivilize" Huck, as he puts it. Although he dislikes the restraints society puts on him (i.e. stiff clothing, education, and religion), he prefers it to going back to living with his drunken father. However, his father kidnaps him and locks him up in his house. Therefore, the first major chunk of the novel focuses on the abuse Huck experiences at the hands of his father--abuse so bad that he must fake his own murder in order to escape alive.
After staging his death and running away, Huck meets up with Jim, a runaway slave from the village. They decide to travel down the river together. Both of them are running away to gain their freedom: Jim from slavery, Huck from his father's abuse and the Widow Douglas's restrictive lifestyle (although Huck does not see it that way yet). For a major part of their journey together, Huck views Jim as property.
Jim becomes a father figure--the first Huck ever had in his life. Jim teaches Huck right and wrong, and an emotional bond develops through the course of their journey down the river. By the last segment of the novel, Huck has learned to think like a man instead of a boy.
This change is most poignantly demonstrated when we see the melodramatic prank that Tom Sawyer would have played with Jim (even though he knows that Jim is already a free man). Huck is genuinely concerned with Jim's safety and well-being, whereas Tom is only interested in having an adventure--with complete disregard for Jim's life or Huck's concern.
Tom is still the same boy as the one in The Adventures of Tom Sawyer, but Huck has become something more. Experiences that he has shared with Jim on their journey down the river have taught him about being a man. Although Adventures of Huckleberry Finn contains some very poignant critiques of slavery, discrimination, and society in general, it is also important as the story of Huck's journey from boyhood to manhood.