For me, Heyer books are all about discovering character through dialogue, and this is just as rich as the others. Right now, though, I've been reading to see how she uses history in her stories, and this one is a little weaker in that respect--the details are sharp as ever but they don't really mean much to the story or push the characters' growth. This story could have been told anytime in wartime when the stock market is volatile.
When Jenny becomes pregnant (a logical event when one marries to continue a dynasty), I was shocked. The couple still spoke to one another at such a remove that I couldn't imagine they had ever shared "pillow talk." Also, for me, Dev came off as yet another selfish, self-satisfied protagonist while Jenny, a strong woman, seemed to be using her strength to convert herself into a dishrag.
The "love the one you're with" story is tricky in romance; I'm glad she went for it with such honesty. I wish we (as romance writers and readers) would allow ourselves the same range these days.