How is the story uncertain..( somebody has already answered this but I need full answer for my exam) thanks..

This has been answered:

We are left to wonder about a number of sespenseful narratives for much of the book, the main one being over Muff Potter, the town drunk who is framed for the murder of Dr. Robinson. Although his kind nature and drunken state make him harmless, Potter is persecuted by the entire town that believes that he is a murderer. Tom and Huck know the truth but are afraid of the Injun Joe.

Also we we wonder if Becky and Tom make it out of the cave.