I never read the adventures of Tom Sawyer and so started Huckleberry Finn not knowing how Huck made his fortune. As it turns out, it doesn't matter. Huckleberry Finn runs away from home and leaves that fortune behind him as he goes sailing down the Mississippi on a raft with a runaway slave, Jim.
The plot is a mixture of comedy and tragedy and farce and the book is at turns charming, quaint and funny. Twain creates humour through situations, through speech and through piercing observation of human nature. Mixed in with the adventure story of Huck's travels is a picture of American fronteir life in the south in the 1800s. Twain has been criticised for this book, but underneath the shenanigans and wry laughs is a serious message about stereotyping, morality, the interaction of self and the community and, perhaps most importantly, friendship and racism.
What you won't find is plot development of any sort. Apparently in the first editions of the book Twain himself warned against looking for a plot. The raft on river device enables him to string together a series of humourous situations as the characters reach new towns without the need to develop the plot in any particular direction. When Huck reunites with Tom Sawyer the pace drops as Twain gets a bit carried away in the larkishness of the boys.
Twain has written the book in the first person diction of a southern American waif which may give some continental readers difficulty at times. The characterisation of Huckleberry and Jim and those he meets along the river are all consistent and believable.
Not a bad synopsis
and for further exploration, one can consult the source material right here on EveryAuthor:
http://www.everyauthor.com/writing/books/mark_twain
Cheers,
Béla