Critical Analysis of Huckleberry Finn The Adventures of Huckleberry Finn by Mark Twain describes the journey of a young boy and a runaway slave, Jim, up the Mississippi River. One of the most important themes of the book is that society is cruel. The book's tone also changes. Sometimes its serious, other times its funny, even silly. The book is classic because the tone surprises and intrigues the reader while the themes teach the reader moral lessons. While Huck is on his journey he realizes that society is cruel. An example of this would be when Buck tells Huck, "A man has a quarrel with another man, and kills him; then that other man's brother kil