I've started this review three times and deleted it right back to nothing. I really can't find the words to describe how astounding it is. The raw emotion of it still has me in its grip. Several times this book had me in floods of tears. 
 Lots of the other reviewers go over the bones of the plot, and the conceit of it, so I'm not going to do that. What I'll say is this: if you're considering reading this, go to a bookshop and read the first few pages. You'll know by page ten whether you'll be able to put it down again before you've finished - I couldn't.