I picked this one up because I thoroughly enjoyed ADDICTED and was very intrigued about the spinoff story of Wallinford, but having finished must say that for me SINFUL definitely fell flat.
I love Charlotte Featherstone's vivid and emotion-laden prose, but felt that the beginning of the book when Wallinford was under Jane's care just did not work. The very crucial relationship building that was needed to carry the story was far too rushed and I just could not find it believable.
Animal lust does not just magically transform into love. I think if events had happened more slowly, it might have worked, but it didn't... and didn't. Thus, in this book I couldn't help feeling the sex was far too gratuitous and the spinster heroine succumbed far too quickly and easily.
I liked Jane's character for the most part, but felt she kept contradicting herself. Wallingford was a tortured hero with a pretty nasty secret. He had much to overcome but the set up was not credible for me.
While I will definitely read this author's other books, I just wasn't crazy about this one.