My grandmother (who has perhaps the most insightful literary taste of anyone I know) gave me I Capture the Castle when I was about 12 and I've never outgrown it. The story centers around the Mortmains, an upper-crust British family who've lost their crusts and are languishing in a decrepit castle.
The father wrote a well-received novel ten years back and has been blocked ever since; Topaz, the step-mother is a clothes-shy hippie (before there was such a thing), Rose, the older sister, is beautiful, knows it, and wishes she lived in a Jane Austen novel, and Cassandra, the sharp-witted younger sister observes (and narrates) all in her diary, and Stephen, the "godlike" servant, worships Cassandra despite her platonic feelings for him.
After a wealthy American family with two dashing young sons become the Mortmains' landlords, circumstances become a bit more lively, and fraught with passion. While some references are dated, Dodie Smith's (who also wrote 101 Dalmatians) language isn't the least bit florid or stuffy; Cassandra's voice is witty, honest, and very real. Check it out if you're in the mood for a romantic romp with sides of history and culture.
[Image via Reading Rants]