Give the details of their plan?

Tom chances to come across Joe Harper, also crying for similar reasons. Joe, whose mother had whipped him for drinking cream (a crime of which he was innocent), is in tears and has decided to lead the life of a hermit; but after Tom's persuasion, Joe agrees that a life of crime would be more desirable. So the two boys, determined to become pirates, plan to run away from home and live on Jackson's Island: an uninhabited, narrow, wooded island in the middle of the Mississippi River.