June 1944. The Normandy landings—the largest amphibious operation in history—are already in the works, and any delay risks exposing the Allies’ plans to German intelligence. James Stagg, Britain’s chief meteorologist, must convince the entire Allied high command, led by General Dwight Eisenhower, to trust his unconventional methods and change the operation’s plans. The scientists have only 72 hours to accurately forecast two approaching storms at once, but the fate of the entire Western Front depends on it.