what object in this chapter leads to a real mystery later on in chapter 3?

Do you mean the file with which the convict tries to take the chains off his legs?  He works diligently to get them off.

i have to read the book too and it is a very slow process trying to read it and answer multiple vocabulary words and questions with it, besides that i think it might be what connection the two convicts have between each other will lead to a mystery. i'm on chapter 32 right now so i know what's going to happen, but yea that's just what i put

also, i'm only in 9th grade now lol and i added two links to my quizlet thing with all the vocabulary and a summary of the book that i had to do for my school but idk if it will be the same for you.