The Round House meanders but then comes back into focus in the last chapters

Louise Erdrich's The Round House got off to a great start and then meandered in the middle chapters but is coming into focus again in the last section. What happened? Well, Erdrich set up a very intriguing plot with the narrator, a teenage boy, describing an assault against his mom leaving her severely beaten and traumatized - and the narrator (Joe) and his dad, a judge, set about in their different ways in tracking down the assailant. The middle section of the book is kind of a mess, though, as, among other things, Joe comes across too many clues too easily, ultimately he learns about the assailant not through his assiduous sleuthing but when his mother, emerging from her trauma, pretty much tells everything - a very weak narrative device, and third Erdrich gets distracted, or at least I did, by a number of side plots, some very funny (the old Indians talking about their sex lives, e.g.) but other elements either confusing (the governor's plan to adopt an Indian baby?) or highly tangential (a few Indian legends worked in - although these are fun to read, even if they don't contribute to the forward movement of the story). In the final chapters of the book, though, Joe, angered that the assailant has essentially been let go without punishment (You, who philosophize disgrace ... ), decides to take vengeance into his own hands and prepares to ambush and shoot the guy who attacked his mother. It doesn't seem like this is something that can come off - the plan relies on a lot of shaky elements, like stealing a gun and hoping to get the timing just right to ambush the guy, Linden Lark, on a golf course, but we're now quite riveted to the plot and eager to see not how Joe will do it but how he will be saved from his worst instincts.