A 1930s Lockheed airliner used by MI6 to spy on pre-war Germany is restored to flight by engineer Richard Grace and his team. To the suspicious Gestapo security men who checked his documents and searched his plane, maverick Australian pilot Sidney Cotton was on a business trip to promote his film business. In reality, he was Britain's most audacious spy, photographing Hitler's military secrets from the air - and on one occasion, with a Nazi general in the cockpit. The restoration reveals tell-tale signs of the plane's top-secret past.