I've read several of Barbara Willard's books, and the Lark and the Laurel is really the beginning of the Mantlemass Chronicles. While the language may be a bit difficult for teenage (14 and up) readers to plow through, the historical descriptions and politics that play out in it are wonderful. (And accurate from what little I've read of the period!) Social customs, class structures and well-worded descriptions of late medieval to early renaissance England fill her books. If you like this series, I recommend reading the Brother Cadfael series by Ellis Peters, or any of Sally Watson's books.