Let me start off with a warning: even though this book is very good, and well deserves its Edgar, perhaps reading it will not be the best thing for you.
For one thing, its narrative structure requires some attention from the reader. The action on which the narrator reflects takes place in the 1920's. The point of view shifts between the present and a moving index in the past, an index which inexorably creeps up on the disaster. Meanwhile we are given misleading hints and scraps of information about what will happen. Actually, the narrative is not so much like seeing one thing, then another. It is like watching a dithered image come up on your computer screen: first you get rough outlines, then the details are filled in, until finally all the pixels are filled in. But the last pixels are the important ones, in this case.
Most intelligent readers can handle that kind of variation from normal style, but some can't, and if you can't you should read something else. But that's not the main danger. Once the details are all filled in - on the last page - and you get a good look at the picture, you will not be happier for it. It will be sort of like one of Dore's engravings for Dante's "Inferno": a very well done picture of something horrible.
I am using the words "horror" and "horrible" in a very deliberate sense. I don't mean in the Stephen King sense of non-human ghouls and monsters. What I am associating with the word "horror" is a sense of inescapable disaster befalling people who don't deserve it, and for no reason that you will find at all compatible with the notion of a "fair universe". It's not enjoyable to look at, and that's why the craft of horror writing often involves sneaking up on the reader and sticking it in his/her face before he/she can get away.
Well, after you have allowed yourself to care for the characters - and there are no villains in the piece - you will, at the end, find out who dies, and how, and who suffers, and how, and why. And it will be a very bleak picture - a picture of great artistic integrity, but without any pleasant highlights whatever. And there is a distinct possibility that you will say to yourself, "Why did I read this? Why did I look upon this picture, which will now depress me for the rest of the day or longer?"
I'm really not kidding about this. However, on balance, I am glad I read this book. It is, in fact, a horror novel about ethics. The disaster which envelops the narrator (then an adolescent boy at his father's private school on Cape Cod), and the teachers he loves, and everyone and everything else he values, is ultimately one of conflicting imperatives. Conform to hidebound convention, or cast it off? Follow your heart, or lock it away? Do your duty, or abandon it? Help your loved ones, or remain aloof? Mercy, or accountability? St. Augustine, I think, made the point that sin is virtue perverted or overdone. Therefore, the mere fact that you are acting on an ethical imperative is no insurance that you won't have blood on your hands. But to know what virtue has been perverted into what catastrophic sin by whom, you have to wait for the last pixel.