I haven't done my research but this feels like one of Heyer's more mature contributions to her body of work. There are no wild romps through the English countryside or dramatic revelations of Love All Along. Jenny, the heroine of this story, is distinctly unattractive, especially in comparison to the hero's beautiful first love. She is remarkably clearheaded, though, and one of Heyer's sweetest and most generous characters. Adam, the hero, responds admirably to his various trials and duties, but does not fall head over heels for Jenny. They get on all right.
There's probably a lot more to say about the relationship between Adam and Jenny. Yet, once again, Heyer's side characters constantly threaten to steal the spotlight. Mr. Chawleigh, the heroine's father, looms larger than any other character in the book and booms right off the page. Lydia, the protagonist's sister, is an absolute delight. I would have loved to read a book where these two teamed up and set London by the ears, while Brough just looks on in amused resignation.
I really liked A Civil Contract
. It's more realistic than any of Heyer's other books, but it ends on a quietly hopeful note.