With 72 hours remaining until the Normandy landings, the fate of the world hinges on… the weather. War is about more than just battles; it is defined by strategies and decisions that can impact millions of lives. James Stagg (Andrew Scott), a meteorologist working for the British Army, faces the most critical decision of his career: the forecast he delivers could determine the success or failure of the greatest military operation in history. Amidst an atmosphere of mistrust and intense pressure from top commanders, Stagg wages a psychological battle against the clock, supported only by Captain Kay Summersby (Kerry Condon). Overseeing it all is General Dwight D. Eisenhower (Brendan Fraser), who must decide whether to launch the invasion or delay it—risking the possibility that the Germans might discover the Allied plans.