The Enigma Game by Elizabeth Wein
In 1940s England, fifteen-year-old Jamaican British orphan Louisa Adair takes a job as caregiver for an elderly German woman living in Windyedge, Scotland. Wanting to do something more for the war effort, Louisa befriends Ellen McEwen a volunteer with the Royal Air Force, and Jamie Beaufort-Stuart a flight leader for the 648 Squadron after a German pilot lands in their village and leaves an Enigma machine and key that translates German code. Together the three teens work to understand the puzzle that could help sabotage the Nazi war effort.
Review from School Library Journal:
This World War II novel is an exhilarating and atmospheric read. Set in 1940 in a small Scottish village on the North Sea that is home to a Royal Air Force base, the narrative features alternating voices, daring action in the air, and high-stakes intrigue on the ground as a variety of young people work to undermine and bring down the daunting German war machine. The young people's lives and stories converge when a German pilot lands in Windyedge and leaves behind a mysterious box—an Enigma machine—and, more importantly, a key to how it works to translate German code. A lengthy "Author's Declaration of Accountability" outlines Wein's research and representation, and provides further reading and numerous interesting links.