This was actually more like a 3.75 for me. But I think it's more a matter of personal taste.
First the plot. Robert Hawthorne has been incarcerated in virtual isolation and total anonymity for eight years while his twin brother, John, assumed Robert's role as the Duke of Killingsworth ... as Robert. Sending letters back to himself from America from his "brother", Not-Robert AKA John, has managed to make everyone believe his ruse.
Robert manages to escape after eight long years and returns to take his place. Fearing a return to the 'new prison system' if he's discovered -- since it will be only his word against the guy who has had all of the ton
believing he's the Duke for eight years -- Robert sends his brother back to the prison (with the dishonest warder who'd collaborated in Robert's incarceration) in his place rather than trying to make his case right away. He's a bit discombobulated, which is understandable. I'm discombobulated just trying to explain it, which makes Heath's abilities that much more impressive.
So, Robert wakes up the next morning in a nice, soft bed with clean sheets only to find out it's his wedding day. Holy moly!. Oh well, he assumes it's a typical arranged marriage and goes through with it, only to find he's wed a lovely girl who seems to have stars in her eyes over him ... or his brother ... who was him when he asked her to marry him ...
It's all very understandable in the book, though, and Robert's dilemma is pretty clear. Except that he's feeling much more kindly toward John than I think is believable. He wants to find a way to prove his identity while not touching his new bride so she can eventually go to John, whom Robert believes she loves. Meanwhile Torie and the real Robert are falling in love with each other. She barely did know John/Robert after all, even though she liked him and had anticipated a lovely marriage, but there was no actual love involved in their courtship.
I did think, right away, of a few ways Robert could prove his identity, which was a bit annoying since he couldn't come up with anything and it kind of went on and on. In fact, we got fully through 60% of the book and nobody else knew his story. Which is where my grumble comes in. Because he was the only person who knew his problem, there was a lot of introspection going on. And since he was trying not to give himself away, Torie's part was mostly isolated as well. I'm kind of an action/dialogue girl, and that's why I say my problems with the book most likely have more to do with my taste than with any real gripe about Heath.
As always, her writing is engrossing. The characters are interesting. The chemistry works. But I felt throughout that things really couldn't happen until SOMEBODY knew his secret and I feel I was right. When someone figures it out, things really do start to take off. But that's after 60% of the book is gone.
The ending is quite nice and the couple is lovely. I don't know if they appear in any other stories, but I'd like to know more than the epilogue told me about their ongoing life and what happens with John. Like Robert, I never understood why John hadn't just killed him.
So, Heath comes through in the end, but I would have preferred 'sunlight' earlier and a more thorough resolution. But the characters and romance are good, as one can expect in a Heath novel, and there are a couple of laughs as well -- even with the sometimes dark subject matter.