Code Name Verity is the story of a friendship formed between two young women, Julie Beaufort-Stuart and Maddie Brodatt, during the early years of World War II. When the story opens, it's November 1943, and Julie is a prisoner of the Nazi Gestapo in Ormaie, a city in Nazi-occupied France.
Believing Maddie to be dead and having decided to exchange information in return for more time to write her story, Julie begins a long, detailed confession of everything she knows. However, Julie buries any information that would be of military use to the Nazis inside the story of her friendship with Maddie and how Maddie came to be the pilot who dropped Julie in France before crashing her damaged plane. Part 1 ends with an order from a high-ranking Nazi for Julie's execution.
Maddie takes up the narrative in Part 2, and she has lots of surprises for us, the first of which is that she's not dead—she did crash the plane after Julie parachuted out, but she survived. Stuck in France without appropriate identity papers, though, Maddie is in serious trouble. Oh—and she wasn't supposed to be flying into France in the first place. Oops.
Fortunately, she falls in with a Resistance circuit known as "Damask," the circuit Julie would have worked with had she not been captured early in her mission. The people of Damask help Maddie hide in plain sight by providing her with a false identity, and as she waits for a British refugee flight to get her out of France, she starts working with the group to find Julie and complete Julie's mission. Meanwhile, she writes Part 2 in her pilot's notebook in order to record details of the crash.
Maddie discovers that Julie will be transported, along with other prisoners, so Damask sets up an ambush to free them. The ambush goes terribly wrong, though, and unable to free her friend, Maddie shoots and kills Julie herself before the Nazis can begin torturing her.
One of Julie's interrogators turns and works with the Resistance—yay—and she delivers Julie's papers to Maddie. Maddie works out the information Julie embedded in them and uses it to help the members of Damask complete Julie's mission, which was to blow up the Ormaie Gestapo headquarters. She also discovers that Julie's "confession" is total lies, except for the parts about their friendship, and that Julie never told the Nazis anything of value. Part 2 ends with a letter from Julie's mother, telling Maddie she did the right thing and asking her to be like the daughter she lost.