It reminds me a little bit of The Book Thief, in that it's set in World War II, and in that it will, in certain moments, emotionally destroy you, put you back together again, and leave you slightly unable to function as a person after you've finished it. But in a good way. In the sort of way where you're really glad you read it, and want everyone you know to read it as well.
Code Name Verity is the story of two British young women during the Second World War: Maddie, a pilot, and the girl code-named Verity, who is a "special operative." Verity has been captured by the Nazis in France, and she has been given two weeks to write down everything she can remember about the war effort in Britain. In doing so, she tells the story of herself and her best friend during their time in the Women's Auxiliary Air Force, and how she came to be in France.
It's impossible to say any more than that about the story without spoiling it. It's intense and wonderful and you need to go into it blind, not least so that you can finish it and then feel the need to read it again immediately, to piece together all the things that you missed. It is unlike anything I have ever read, full of pain and bravery and friendship.
If you go looking for it, you're mostly likely going to find it in the YA section. I don't understand why, as the main characters aren't teenagers (by my best figuring, they're in their early-to-mid 20s). So if you're not generally a fan of YA, give it a try. If you're not generally a fan of historical fiction, give it a try. And if you want a book about two best friends who feel beyond real (even if that realness is painful at times, considering the setting), then run run run to the bookstore right now. It's a slow-burning sort of book in the beginning, and I didn't quite get what the fuss was about for the first fifty pages... but once you're immersed in it, you won't escape it unscathed. And you won't want to.