Code Name Verity by Elizabeth Wein (Hyperion hardcover, 15 May 2012).
I cannot begin to describe how much I loved this book.
It's the story of a young Englishwoman, whose name we don't know for some time. Flying into German-occupied France in 1943 on a secret mission, her plane crashed. She was captured by the Germans and imprisoned in a former castle, and she believes the female pilot of the plane was killed.
She begins from the very beginning with the story of how she became involved with her country's war effort, and as she progresses, we learn not only her name, but a great deal more about her life.
It's difficult to say much more about the story without giving away too much, so please believe me when I tell you that it's an absolutely mesmerizing tale. Despite wanting to continue reading as fast as you can to find out what happens, you may find yourself putting down the book just so you can absorb what the young woman and her compatriots experience, the insanity that they begin to perceive as normal.
This book is a departure for author Wein, who previously has written fantasy novels aimed at young adults, and judging by the number of 2012"best" lists it was on (it would certainly have been on mine had I finished it in time), she's been remarkably successful.
FTC full disclosure: I won this book in an online contest.