Tamsin, by Peter S. Beagle
This exquisite book tells the tale of a New York City girl moved to the depths of the English country-side. Her tale is one of fantasy, full of creatures the likes of which you've never heard of. Her family attend to repair their new home, which has much deteriorated with age. The main character, Jenny, and her cat, Mister Cat, soon learn that this house is more than it appears. I would recommend this book to all teens.