Very sad! Mary Stewart is one of the first authors I discovered when I sneaked into the adult part of the library when I was about twelve. The first book by her that I read must have been Madam, Will You Talk, which remains a firm favorite to this day. Stewart always wrote about interesting locales (the Pyrenees, Corfu, Lebanon, among others) and had a unique gift for bringing the landscape with its smells and sounds to life. I also adore her characters, who are strong but not snooty or overbearing (well, the heroes may try once in a while, but don't get away with it
).