This extremely funny and well-characterized Regency romantic comedy was the novel which got me hooked on Heyer, and it's still one of my favorites. I also think it's objectively one of her best.
Crotchety, penny-pinching Uncle Matthew announces that he is leaving his entire fortune to his fun-loving adopted daughter Kitty-- on the condition that she marry one of his many nephews. Kitty is violently opposed to marrying any of them, especially the handsome rake Jack, but she doesn't want to be left penniless either.
So she hits upon a cunning plan: she'll get her cousin Freddy, who has his own money and no romantic interest in her, to enter a sham engagement with her while she tries to figure out what to do-- and gets to live it up in London in the meanwhile. Kitty, Freddy, Jack, and numerous cousins, evil aunts, French gamblers, damsels in distress, cynical fathers, be-measled brothers, and practical women of low breeding all proceed to collide in London.
You don't have to be a fan of romance to love this book, as it's more of an intricate comedy of manners bordering on farce than a traditional romance-- in fact, all of the intersecting romances in the book are rather atypical.
The ideal reader for the this novel would have read enough romances-- possibly even enough other Heyers-- to have an idea of certain romantic conventions. That ideal reader will be surprised as well as delighted at the way Heyer turns a certain romance convention upside-down, and so creates the only Regency romantic hero who I would actually want to marry.
The more Kitty protests that she hates the rake, the more the reader thinks, "Yeah, right." But as the book goes on, not only does Jack (the rake) start seeming like a jerk, albeit the sort of jerk who is often portrayed as a romantic hero, but Freddy starts seeming like a really great guy. He's not a romantic hero type, being a dandy and unromantic and a lightweight, but he has a kind heart, excellent taste in clothes, a canny sense of how to navigate tricky social situations (a genuinely useful skill), and a surprising amount of common sense. What's more, Freddy and Kitty suit each other far better than Kitty and Jack, and seem like they'd be happy together.
But Freddy's not a romantic hero. Men like Freddy never get the girl.
So when, at about the halfway mark, I began to realize that Heyer knew Jack was a jerk, and that the likable sidekick was the hero after all, I wanted to stand up and cheer. How often does a book make you feel like that?