Considering how elegantly simple this film is, I thought the plot points would be easy to identify. Alas. Here are my best guesses based on Toby’s goal, which is to steal enough money to save the ranch from the bank.
Act One: Toby and Tanner rob two banks while Texas Ranger Marcus Hamilton laments his impending retirement and needles his partner. The act ends on p.18, with the conclusion of the scene at the ranch. While there’s no big event marking the end of the first act, at this point, everything is locked into place — Toby and Tanner will be robbing specific banks all week, while Marcus and Parker will attempt to catch them — and we have a general idea of the main characters and their needs/wants.
The midpoint (?) is when Toby goes outside and looks at the stars, p.64. Besides the transition into the next day, there’s no real event here, but after this point, the story ramps up as we start to find out specifically why they’re robbing banks in the first place — there’s oil on the property, Toby creates a trust for his sons, and they have to pay off a lien…by Thursday. Now that they have most of the money, they start doing something with it.
All Is Lost/End of Act Two: the bank robbery in Post, p.86–89. Because Tanner kills two men, what was a “noble” bank robbery has become a much more serious crime, moving beyond Toby’s simple plan. He’s totally freaked out…can he pull himself together to finish it?
It seems to me the final struggle happens at First Texas bank, when Toby pays off the lien, overcoming the banker who’s seemingly trying to stall. If his goal is to save the ranch for his sons, then he’s accomplished it here, and it no longer matters if he gets caught.
So then, the scene with Marcus at the end is the denouement, where both men somewhat make peace with each other by agreeing neither has peace for what they’ve done.