Mysteries Set in a Country House

Margot Kinberg, on her excellent blog, was talking about mysteries set in a country house the other day. I tried in vain to come up with an American one, but I couldn't think of one. It may be because the country home, where the upper classes can hunt and ride, is more a part of their social class system than ours.

I think Americans with a second house are more prone to have the house at the beach or in the mountains. Can you think of a US mystery set in a classic country house? There must be some from the days when the beach and skiing were not as prevalent.