Code Name Verity by Elizabeth Wein
Two young women from totally different backgrounds are thrown together during World War II: one a working-class girl from Manchester, the other a Scottish aristocrat, one a pilot, the other a wireless operator. Yet whenever their paths cross, they complement each other perfectly and before long become devoted friends. But then a vital mission goes wrong, and one of the friends has to bail out of a faulty plane over France. She is captured by the Gestapo and becomes a prisoner of war. The story begins in "Verity's" own words, as she writes her account for her captors. Read a sample.