I'm wavering between a 2 and a 3, because honestly I just wanted to stop reading at so many points but then again, I kind of liked the premise and the worldbuilding?
Like okay, the main character Sarn isn't exactly unsympathetic. There's so much going on in his life and so much that he's struggling through, that you just want to give him a hug and tell him it's going to be okay, you know? But then again he is also annoyingly stubborn and idiotic that you also want to just slap him upside the head and tell him to just grow up.
Seriously, 90% of this book would have been better if Sarn just opened his mouth and explained something. Or if an editor went through the book and said, "yea, this theme/scene has been repeated one too many times, let's delete it and move on with the plot." Because by GOD it is repetitive, even down to individual sentences. Yes, Sarn doesn't trust anyone. Yes, the Rangers are terrible people who don't like Sarn. Yes, everyone AND magic are out to get Sarn. Yes, no one is supposed to know about his son. Yes, Sarn has no idea what is going on and he has to solve it without anyone else knowing...
And that's the biggest flaw of this book. Because Sarn doesn't know what's going on, and he doesn't ask anyone for help, and he just doesn't listen to anyone else either, the reader spends the first half of the book being as confused as Sarn is as to what is going on and I dunno about you but that is super annoying.
You could probably start reading in the middle of the book and still catch what's going on because a lot of it is repetitive. And you'd reach the resolution much faster. The thing is, the end resolution and the intricacy of the actual mystery was like. WOAH. That's actually quite cool. Except, it comes out in a rushed couple of chapters and you don't get a proper lead-up to appreciate it because it was never properly explained (because Sarn. doesn't. say. anything. Even to the readers).
There were many supposed "clues" dropped earlier in the book, but those clues were more like vague hints, e.g. "something was different about the room, but Sarn couldn't tell what because he was so tired" (or something like that) And later on, you find that someone had actually carved a rune or charm on the floor that allowed the bad magic to enter. But all you know is "something is wrong" which is SO helpful in a book that is all about "something is wrong."
TL;DR: Ideation good, execution not so good.