A German soldier risks his life to drop off the sought-after Enigma Machine to British Intelligence, hiding it in a pub in a small town in northeast Scotland, and unwittingly bringing together four very different people who decide to keep it to themselves. Louisa Adair, a young teen girl hired to look after the pub owner's elderly, German-born aunt, Jane Warner, finds it but doesn't report it. Flight-Lieutenant Jamie Beaufort-Stuart intercepts a signal but can't figure it out. Ellen McEwen, volunteer at the local airfield, acts as the go-between and messenger, after Louisa involves Jane in translating. The planes under Jamie's command seem charmed, as Jamie knows where exactly to go, while other squadrons suffer, and the four are loathe to give up the machine, even after Elisabeth Lind from British Intelligence arrives, even after the Germans start bombing the tiny town ...