The Husband's Secret

This is honestly one of the best books I have ever read in my life. I was engrossed in the story from start to finish, and the ending was one of the most shocking and heartbreaking endings I have come across, even more than some Agatha Christies I've read (which is saying a lot, she is my favourite author and I've read most of her books).
This is the book that got me into Moriarty and has kept me reading every subsequent book since. I still think about this one whenever I recall my favourite books, even though I read it years ago.