In the summer of 1940, following the fall of France, Britain stands alone against the might of Nazi Germany. With the British army depleted after the Dunkirk evacuation, the country's last line of defense is the Royal Air Force (RAF). The Luftwaffe, the German air force, embarks on an aerial campaign to gain air superiority over the English Channel, which is necessary for Operation Sea Lion, the planned invasion of Britain. The Luftwaffe targets RAF airfields, radar stations, and aircraft factories in an effort to cripple British air defenses.

As the battle rages in the skies, RAF pilots from various backgrounds, some veterans and some just out of training, are thrust into relentless combat. They fly Spitfires and Hurricanes, constantly taking to the air to intercept massive formations of German bombers escorted by fighters. On the ground, the effort is supported by a network of ground crews, radar operators, and the women of the Women's Auxiliary Air Force, all working together to repair aircraft, plot enemy movements, and keep the pilots flying. The British resolve is tested to its limits, as the fate of the nation hangs on the courage and tenacity of these airmen against overwhelming odds.