The hair stood up at the back of my neck. Those letters meant something. And with the cipher machine, I'd worked it out myself.

1940. Facing a seemingly endless war, fifteen-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 action. 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 with the Royal Air Force, 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 cross-hairs of the enemy.

Featuring beloved characters from Code Name Verity and The Pearl Thief, as well as a remarkable new voice, this brilliant, breathlessly plotted novel by award-winning author Elizabeth Wein is a must-read.