Lippman's freestanding novels are not your standard mysteries. (She has also written a series featuring a PI named Tess Monaghan, of which I've read part of one, that I'm not really interested in pursuing.) Yes, there's been a crime committed, and there usually are police involved, but her writing spends more time digging into the minds of the people involved, and looking at how their histories have led them to be connected to the crime in some way.
I remarked to a friend as I was reading this that it wasn't really grabbing
me, and it never really did, not in that stay-up-all-night-to-finish way. Yet I couldn't put it down, and not because of my usual compulsion to finish a book no matter how dreadful. (e.g., the James Moore book I read recently, which I can't even justify donating to the library book sale. I don't think ANYONE should have to read it, it's that bad.)
The "Three" of the title are three girls, high school seniors, who met in third grade and have been virtually joined at the hip from then until about a year before the book opens. Before the first chapter closes, one of them is dead, one near death, and the third injured, in superficially straightforward circumstances that nonetheless raise the suspicions of the investigating officer. The story of their trio, what brought and kept them together and what tore them apart, set amid the petty politics found in any high school, is the larger mystery at the heart of the book.
I'm not prone to obsessively looking for clues as I read in order to determine "whodunnit" before the author takes me there, so I can't really say whether I could have
figured it out if I'd been paying attention that way - I had a pretty good idea where we were headed, but the "reveal" tied up all those annoying loose ends very tidily. And no one lived happily ever after.