Britain in the summer of 1940 has just watched its army escape Dunkirk while France collapses, and this film covers the scramble that followed: how the Royal Air Force readied itself for the German assault that would become the Battle of Britain. It traces the buildup through Fighter Command's radar chain, the Observer Corps network, and the pilots and ground crews thrown into a defense system built in a hurry against an enemy with more aircraft. Archival footage of Spitfires and Hurricanes on the ground and in formation is paired with newsreel material from the period, alongside expert commentary that lays out the strategic choices Air Marshal Hugh Dowding made about when and where to commit squadrons. The film treats the run-up to the battle as its subject rather than the battle's famous dogfights themselves, focusing on airfields, command structure, and the weeks of preparation that decided how Britain would fight when the Luftwaffe finally came. It ends on the eve of the offensive, with the system built and waiting.