In preparation for Operation Overlord, the Allied invasion of Nazi occupied territory, the 'overlords' were the few Allied agents who knew the details of the operation. When one them is captured by the Germans, a double agent must infiltrate occupied Paris, with the help of a high level German officer and the French Resistance.

Ireland, June 1944. The crucial decision about the right time to start Operation Overlord on D-Day comes to depend on the readings taken by Maureen Flavin, a young girl who works at a post office, used as a weather station, in Blacksod, in County Mayo, the westernmost promontory of Europe, far from the many lands devastated by the iron storms of World War II.