In Chapter 2 Tim (the narrator) explains to the reader his community's perspective on the war, then talks with his father about what Sam wanted and then with Sam and Betsy Read about the reasons for the war.
In Chapter 3 Tim describes life at the start of the war, and then gets word from Betsy that Sam is back in the area, so he can see his brother.
In Chapter 4 Continental soldiers come to the tavern and try to take Tim's father's rifle, which Sam had taken with him. Tim runs to get Sam.
In Chapter 5 Mr. Herron asks Tim's father if he (Mr. Herron) can hire Tim to carry business letters; Tim's father says no, because they must be war-related.
In Chapter 6 Tim decides he wants to carry the letters anyway, for the adventure (and money). However, he runs in to Betsy Read on the way, and she opens the letter, which was just a test to see if he was reliable (which he obviously wasn't).