This is a love story told backwards, in the most beautiful manner, so that we know from the very beginning that Emily and Robert love each other enormously, and that he is about to break her heart in the most dreadful way in order to protect a secret that they've lived with for decades. Seeing their love unfold in reverse is beautiful. We get to know them once they have already gotten to know each other, and it makes for an unusual and interesting structure. The secret they hold is referred to throughout, but it isn't revealed until very late in the book. I'm guessing very few readers will figure it out. Even once you know, you want to go back and read the whole story again in the light of the information you now hold.