Because Hart is a really odd character, as introduced in those books. He's the duke so that makes him autocratic and dismissive. He also seems to have zero sense of humor. He kept a mistress who kept a brothel. He's rumored to have non-normative sexual proclivities (and in a novel set in 1880s Victorian Great Britain this really piqued my interest). His first finacee ended their engagement and his wife died giving birth to his son who also died.
Cam's book also introduced us to Lady Eleanor Ramsey, Hart's ex-fiancee and Aisley's good friend. Eleanor is about as far from a conventional lady whilst still being part of the aristocracy as you can get. Her father is nearly destitute, an eccentric scholar of biology/botany/archaeology/you-name-it, and she helps prepare his manuscripts. She has completely withdrawn from whatever society she kept after she threw Hart's ring at him. She knows all of Hart's secrets - and she starts out the book by appearing in London to ask Hart for a job.
Which is just the cover - someone sent her a photo of Hart. A nude photo of Hart. While there is no malice indicated by the sender (no requests for money, no threats), it is odd that someone would take the time to send a nude photo of a prominent politician to his ex-fiancee. Eleanor is willing to discreetly investigate the source of the photos if Hart employs her. Which Hart does - but he doesn't want her investigating the photos. They come from a part of his life that he doesn't want to share with her or anyone. As the two dance around each other, drawing closer together, political issues threaten Hart's life and, by extension, Eleanor's.
The Duke's Perfect Wife was a fun book. Ashley gave it a perfect set-up in the last chapter of The Many Sins of Lord Cameron by letting the family wager on the chances of his success with Eleanor. So the reader - even knowing the marriage plot outcome is a given - also roots for Hart. Ashley also ups the ante by providing the nude photo plot and plenty of chances for Eleanor to describe Hart sans kilt. However, the nude photo plot also makes the novel unnecessarily complicated when the Feinian plot comes into play.
I really only had one quibble with the book - it is really, really hard to understand why Eleanor chucked Hart in the first place. Particularly when Hart mulls over the scene in his mind. I had to read the section three times then go back and read the section of The Madness of Lord Ian Mackenzie where Hart meets Beth. Then the pieces started to fall into place - it wasn't that Hart was possessive or controlling but that he cared nothing for the wishes of others. This does partially translate into Hart's sexual tastes but once that secret is revealed I wondered what the big deal was.
According to Ashley's website there are two more planned books in this series - a book for one of Ainsley's brothers (up next) and one for Daniel (please make him grow up a little bit more, thanks). I'd also like a book, or at least a novella, for Inspector Fellowes and Isabella's sister who got a nice little scene (although their age difference would be the largest of the series - Fellowes is two years older than Hart so nearly 45 while the sister is five years younger than Izzy so approximately 20).
Plothole: The old, abusive duke whom everyone hates (not only because he was abusive but also because he killed his wife - Ian was the witness) seems to have died two ways. In Ian's book it's mentioned that the old duke broke his neck falling off his horse. But in this book Hart's letter to Eleanor reveals that the duke was shot under suspicious circumstances. So which is it?