Gilly was born an incredibly rich duke. Far from trying to get his inheritance, his family did everything in its power to ensure that the sickly little boy would grow to manhood. However, now that Gilly's nearly of-age, their coddling and controlling is less welcome. Being pushed into an engagement with an old friend is the last straw, and Gilly takes an opportunity to flee his hangers-on and pretend to be just a gentleman. While doing so he rescues a fair but dimwitted maiden, takes on the charge of an adventurous boy, thumps villains on their heads, gets kidnapped, burns down a house, and all in all leads a very enterprising life indeed.
I liked this book a great deal. It's largely free of Heyer's love of Regency-era slang, and the main character is far from her usual tall-saturnine-sardonic-controlling hero. The only issue I had was that the love between Gilly and the woman he ends up marrying seems to come out of nowhere. It's a regency romance, Heyer, you've got to put *some* effort into the romance part, no matter how meticulously researched the "regency" part is.