Maybe more like 4.5 stars. I really loved this book. If I am still thinking about bits of it 2 weeks from now, I might upgrade to 5 stars. The idea that "everyone has a double" is problematic for me, but the story and the writing were so good that I didn't worry about it once I started reading. If I needed to just accept that idea to believe in this story, that was fine with me. I loved the first book in this series, and this one was even better. Tana French has the rare gift of creating intricately plotted mysteries that could be just as easily viewed as character studies. Her books are haunting, deep and wonderful.Edited to add: I upgraded this to 5 stars after reading the next in the series, which I really loved, but not quite on this level. I thought about it, and decided that pure genre snobbery had denied this book the 5th star. Was there anything that could have been improved about this book? No, I don't think so. Am I still hearing passages echo in my head? Yes. 5 stars.