London, Spring 1941. Columns of Wehrmacht soldiers make their way along the Mall, swastikas hang from Buckingham Palace and Junkers scream low overhead-a potent symbol of Nazi victory. The Germans have conquered the capital. Churchill and his government have gone into hiding… It’s a chilling picture: What would the Nazis have done if they had conquered Britain? Filmed in England and using Allied and German documents, blueprints, and archive film, this two-part documentary-covering both occupation and resistance-answers one of the most intriguing questions in history. And, for the first time ever, Britain’s plans for defense are unveiled as cameras explore Churchill’s secret wartime citadel and archeologists unearth top-secret bunkers and tunnels.