In the seventy-two hours leading up to D-Day, all the pieces are in place except for one key element: the British weather. Britain's chief meteorological officer James Stagg is called upon to deliver the most consequential forecast in history, locking him into a tense standoff with the entire Allied leadership. The wrong conditions could devastate the largest-ever seaborne invasion, while any delay risks German intelligence catching on. With only his trusted aide Captain Kay Summersby to confide in, and haunted by a catastrophic D-Day rehearsal, the final decision rests with Supreme Allied Commander Dwight D. Eisenhower. With only hours to go, the fate of the war and the lives of millions hang in the balance.