This book is kind of a wild ride and if you're not familiar with Tremblay's work and how freaking dark it can get, it might be a little startling at times. Thankfully I'd read A Head Full of Ghosts so I knew sort of what I'd be getting myself into, but this is a little darker than his previous work so it still threw me for a loop. 
 One of the main things Tremblay likes to play with is the notion of whether or not events in the book are supernatural or not. This is never ever definitively clarified in this book, something that I kind of like. It's sure to frustrate some, but I think that the main reason this works so well for me is that it doesn't really matter if there are supernatural figures in the book because the main issues in the book are human in origin. Early in the book Elizabeth sees an apparition that looks to be her son, but whether or not it's a supernatural visage of Tommy is ultimately irrelevant because what matters is how his disappearance (view spoiler)[and later revelation of his death (hide spoiler)] has effected his family and the world at large. 
 At one point in the book there's mention of a tree located near Devil's Rock and how touching it will summon the devil himself. This is something that kind of intrigued me for several reasons, some of which are quite spoilerish. All I'll say without the spoilers is that it's an interesting comment on the nature of humanity and our propensity for darkness. (view spoiler)[Now with spoilers I have to say that it could easily be argued that it was after that night with the tree that everything continued to grow darker, because I believe that the tree incident happened the first time they met Arnold. At the very least that's when stuff started to go downhill - Tommy started connecting with Arnold more and the boys started keeping more and more from everyone around them, including each other. Perhaps they did summon the devil and rather than him pop out and do obviously devilish things, he instead crept into their minds and silently prodded them into participating in the murder of Arnold's uncle and to participating in the failed attempt to cover their actions by trying to murder Arnold himself. (hide spoiler)] 
 What makes so much of this heartbreaking is the feeling of helplessness while reading the accounts of what happened at Devil's Rock and the boys' interactions with Arnold. You can tell things are wrong with Arnold and with the kids as a whole at the beginning, but there's not much that anyone could really have done about it at the time. The boys had no way of detecting anything off about Arnold nor could Elizabeth, Kate, or any of the other family members of the boys have rescued them, as Arnold was kept a secret from them. It's also easy to see how and why someone like Tommy could be easily manipulated and come to the conclusions he did, as he was just so lonely and awkward that he hungrily accepted whatever scraps of attention and affection he could get, whenever he felt that he fit in. I wouldn't necessarily call him broken, at least not at the start of the novel, but he wasn't far off from that point. Tommy's character hit me a little hard because at times he reminded me a little of one of my nephews, with his love for Minecraft and zombies. 
 To say that I liked the book would be kind of an off thing to say because at times I'm really not certain that I actually liked this book all that much because I would get so wrapped up in the human drama and misery that my heart would sink whenever something particularly bad happened, especially towards the end when the largest revelations come to light. (view spoiler)[Like oh my word, I just wanted to hug Tommy when I read his account of the stabbing and Elizabeth when she was reading the account that ultimately ends with Arnold's unwitting confession that he bludgeoned Tommy to death with a rock, seemingly unaware that he had even murdered the lad. (hide spoiler)] I suppose part of what made it all so interesting was that ultimately we had no reliable narrators for what ultimately happened at Arnold's home or Devil's Rock. Each person telling their tale had a motive for making themselves seem less responsible for what happened, pushing more of the responsibility on someone else. We're ultimately left to decide what or who we want to believe, which is probably why I enjoy Tremblay's books so much and will continue to read - he makes us a full participant by making us care about the characters and then will not give us the entire story, at least not clearly, forcing us to discern for ourselves the truth of the matter.