There is so much you could talk about with this book. I am not sure what the main theme is. Crime? Love? Time? One might think from the title that it would be atonement itself?
As a statement about life starting out at one point and ending up somewhere else completely unimagined, it's a wonderful analogy. We never really know what another person might be thinking or his/her true motives. Even friends. Even family. And there is a certain amount of danger in that. And loneliness.