In the seventy-two hours leading up to D-Day, all the pieces of the stunningly audacious invasion plan are in place except for one key element – the English weather. Britain's chief meteorological officer James Stagg is called upon to deliver the most consequential forecast in history, locking him into a fierce standoff with the entire Allied leadership. The wrong conditions could devastate the largest ever seaborne invasion, while any delay increases the risk of 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.