The premise: What happens in a version of reality where Hannah stays at the bar with Ethan versus the version where Hannah goes home with her friends? I was hooked at least in part because, astronomy enthusiast that I am, I am fascinated with the quantum physics-based idea that for every choice we make, another version spins off somewhere else--so there are countless Allisons for every choice/option that comes up. (That's my layman's understanding anyway!) 
 This was a perfect summer read. I couldn't put it down. Reid's prose is beautiful--light and easy and then double-take inducing as you stumble across something profound. I like that the ending wasn't Sliding Doors-like, but wholly satisfying and believable.