Facing a seemingly endless war, 15-year-old Louisa Adair wants to fight back, make a difference, do something - anything to escape the Blitz and the ghosts of her parents, who were killed by enemy actions. But when she accepts a position caring for an elderly German woman in the small village of Windyedge, Scotland, it hardly seems like a meaningful contribution. Still, the war feels closer than ever in Windyedge, where Ellen McEwen, a volunteer driver at the local Royal Air Force base and Jamie Beaufort-Stuart, a flight leader for the 648 Squadron, are facing a barrage of unbreakable code and enemy attacks they can’t anticipate.

Their paths converge when a German pilot lands in Windyedge under mysterious circumstances and plants a key that leads Louisa to an unparalleled discovery: an Enigma machine that translates German code. Louisa, Ellen and Jamie must work together to unravel a puzzle that could turn the tide of the war … but doing so will put them directly in the crosshairs of the enemy.