July 1940 finds Britain alone, its army's equipment left behind on the beaches at Dunkirk and German bombers already testing its defenses. The film covers the opening months of the Battle of Britain, when the Luftwaffe held the advantage in aircraft numbers and pilot experience and Hitler's invasion barges waited across the Channel for the RAF to be cleared from the sky. It traces how a string of German tactical errors, including the shift from bombing airfields to bombing cities, gave Fighter Command room to recover and rebuild, turning a battle Britain looked likely to lose into a stalemate that broke the invasion timetable. Archival combat footage, wartime newsreel, and maps of squadron deployments carry the account of a campaign fought as much in radar stations and factory output as in the air. Narration sets the strategic stakes plainly: if the Luftwaffe wins control of the skies, invasion follows, and the film builds its case around how close that came to happening in the summer of 1940.