The only reason I read this book through to the end was to see exactly how the heroine would finally reveal her big secret to the hero. (I had guessed what the secret was at some point between the introduction of the heroine and the big revelation.) This secret just happens to be the most important fact in the story and the heroine's character, so it makes no sense to keep the reader in the dark about it until 80% of the book is finished. Getting that reveal so late in the book effectively nullifies every action of the heroine up to that point in the story and totally negates every scene in the book that is told from the heroine's POV up to that point.
Because of this, I felt cheated out of most of the story, and I couldn't relate to how the heroine's feelings for the hero changed from loathing to love. Also, there was no explanation for why the heroine didn't tell the hero about his son a long time ago, which would have been the right thing to do for so many reasons (her loathing the boy's father is not an acceptable reason for not telling him - it's just childish, IMHO).
The author has the heroine decide to become a fabulously successful courtesan after living most of her life in an isolated village in Yorkshire with a decent income and security in her life. I don't know - maybe the author felt this would make the heroine glamorous and attractive to the reader. But really - this is a "career choice" that most women of the time would only have made if they felt they had no other option or they were forced into it, and 99% of the time it was pure degradation. So besides not making any sense at all, the author's decision is totally insulting to the women who had to prostitute themselves simply in order to live.
The spy aspect of the story was pretty lame, and the bad guy was just a 1-dimensional caricature of a really eeeevilllll villain. The melodrama of the last part of the book felt completely contrived.
So - not a keeper and not enjoyable for me.