Anyway, I decided to give SJ Watson's Before I Go To Sleep a go. It was cheap on Amazon for a day and I heard Nicole Kidman praising the book (she was promoting the film) about a woman losing her memory each day. Anyway, I'm rather biased towards Ms Kidman and so tried it.
And it's a very good mystery thriller. I did consider various possibilities, but the one that happened wasn't quite what I expected, and the unfolding of it was brilliant.