The Girl on the Train
I included this book in my "most anticipated for 2015" on one of my podcasts, and it lived up to my expectations, and more. People keep comparing this to other books - Gone Girl and others similar, but I find it quite unique. Also very sophisticated for a debut suspense novel. I had the guilty party pinned down about halfway through, but not motivation or any other details - and I was still 100% riveted until the very end. That's a HUGE compliment. If I have the killer pegged, I usually lose interest, even if I read the whole book.
Besides the mystery plotline, the other parts of the book were an intense character study that was at the same time clever, engrossing, and uncomfortably accurate.
I look forward to more titles by Paula Hawkins in my TBR pile in the future, and they'll move straight to the top as I acquire them. I'm incredibly glad I recommended this to my friends.