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I started off thinking this book was very well-written but too disturbing for me. I felt like I *was* Rachel (despite having far less personal experience with drinking and blackouts), and she lived in my head way too much for comfort. That's a sign of strong writing to me, even if I didn't enjoy it. I was hooked by the story, though, and I felt that her alcoholism worked well with the mystery--it's a strong choice, having her witness something important but be unable to remember it due to her alcoholic blackout.
The ending, however...
[MAJOR spoilers]
...was, to me, a total cop out.
What I respect most in a story is when the answers are there, but the author is masterful enough at showing them to you in such a way that you discount them until the end. Then you find out who did it (or whatever is appropriate to the denouement of a particular story), and you think, "HOLY CRAP. It was right in front of me the whole time." Some perfect examples in movie form: The Usual Suspects
In The Girl on the Train, Hawkins uses a red herring, making you think certain scenes take place between the victim and one guy, when in fact it's another guy. Let's call them the doctor and the neighbor. (I'm trying not to use proper names in case someone is skimming but doesn't want to have their eye catch a spoiler.) Anyway, unless I really wasn't paying attention, she never gives you any clue that the victim is hanging out with the neighbor, not the doctor. She really just sets the reader up to understand (not just to *assume*--but to comprehend the narrative) that the person the victim is with is the doctor. There is also only one instance that I can think of where the personality of the neighbor is called into question at all. So when, in the end, it turns out the neighbor is the perpetrator, it's a surprise, but not the good kind. This is no, "Oh my god, Verbal is Kaiser Soze." Because in The Usual Suspects, it's all right there. If you are paying attention in a way that 90% of people never do, you have everything you need to realize that Verbal is weaving a web of lies. In The Sixth Sense, Haley Joel Osment looks Bruce Willis right in the eyes and tells him he sees dead people. When? ALL THE TIME. It's like he's waving a flag in front of the audience's face, but I know I didn't see it. Then, at the end, I was like, "HOLY SHIT, Y'ALL. It was RIGHT THERE."
Instead, in The Girl on the Train, Hawkins buried the reveal too well. As a reader there is no way you could see the clues ahead of time. Some of the other reviewers stated that they guessed early on who the perp was, because he was the only one who made sense--clearly their minds work differently than mine does. But even so, they chose him by process of elimination, not due to well placed plants by the author. Don't get me wrong, it's no good when you can figure out who did it way before the characters do. But in a well-told mystery, the clues would be there, they'd just be shown to you in a way that made you consider them insignificant. Like in Harry Potter--the cards with the chocolate frogs... tell you everything you need to know about Nicholas Flamel. But I paid no attention to that at all, so at the end I was like, "OMG, Rowling, you are a MASTER."
So I'm left feeling like Hawkins went, "AHA! It was the neighbor all along!" And I'm like, "Huh?" Not a satisfying feeling.