There was a lot to like about this book: the exploration of grief and the immediate post-bereavement period was well handled and written in a confident, engaging style. I also liked the portrayal of the couple's relationship and thought that was realistic and well observed; the transition from the feverish beginnings of the relationship to the weary couple brought together through the shared bereavement was nicely handled.
However, the book's main failing was that the author seemed not to have had the confidence to make the book just that: an exploration of grief and a study of a relationship. Instead, we get a very poorly developed revenge sub-plot, which is farcical, poorly developed and never ignites. Simultaneously the author goes off on yet another ill-advised tangent with the sub-plot of the letters; again, lacking in realism, worthy of a bad made-for-TV movie and demanding a level of suspension of disbelief that I found impossible (the number of times I was rolling my eyes and saying "Oh come ON!"). As a result, the book seems not to know what it wants to be and I think it suffers from that.
And finally, Faber & Faber, get your act together and use some decent copyeditors and proofreaders. The book was littered with spelling mistakes and typos, which I found distracting and which undermined the book. You are left thinking that if the publisher doesn't care about the book enough, why should we?