In the 72 hours leading up to D-Day, everything is prepared except for one crucial factor: the weather in Britain. Britain’s chief meteorologist, James Stagg, is tasked with making the most important forecast in history and finds himself in a tense dilemma with all the Allied leaders. While unfavorable conditions could ruin the largest amphibious invasion to date, any delay carries the risk of alerting German intelligence. The final decision rests with Allied Supreme Commander Dwight D. Eisenhower, who can trust only his confidant, Captain Kay Summersby, and who cannot let go of the memory of a D-Day rehearsal that ended in disaster. With only a few hours remaining, the fate of the war—and the lives of millions of people—hangs in the balance.