The movie opens with an explanation of events leading up to the Battle of Britain beginning in the Summer of 1940; the Battle of France sees British aircraft withdrawn from the skies of mainland Europe as British Prime Minister Winston Churchill declares the war over France lost and the Battle of Britain begun. British officials fear the power of the German army will be too strong for Britain to withstand alone; Royal Air Force officers recall all fighter pilots and planes to mainland England to protect the country from the impending invasion under the German codename operation Sea Lion.
During the Summer of 1940 the battle for control of the British skies is almost lost when British High Command order a retaliatory bombing raid on Berlin in response to Nazi bombing of London. Angered by the bombing of Berlin Adolf Hitler orders a constant bombing of the English capital giving the RAF time to rebuild and regroup. Strengthened by pilots from occupied Europe and Canada the RAF return with large numbers of Spitfires and Hurricanes to reclaim control. September 15th 1940 is seen as a pivotal day in the movie as the British planes drive back a huge wave of German planes that results in Hitler cancelling the invasion of Britain and turning World War II in the favor of the Allied forces.