June 1940. Britain is Europe''s final bastion of freedom - and Hitler''s next target. But not everyone fears a Nazi invasion. In factories, offices and suburban homes are men and women determined to do all they can to hasten it. Throughout the Second World War, Britain''s defence against the enemy within was Eric Roberts, a former bank clerk from EpsomEquipped with an extraordinary ability to make people trust him, he was recruited into the shadowy world of espionage by the great spymaster Maxwell Knight. Roberts penetrated first the Communist Party and then the British Union of Fascists, before playing his greatest role for MI5 - as Hitler''s man in London. Codenamed Jack King, he single-handedly built a network of hundreds of British Nazi sympathisers, with many passing secrets to him in the mistaken belief that he was a Gestapo officer. Operation Fifth Column, run by a brilliant woman scientist and a Jewish aristocrat with a sideline in bomb disposal, was kept so secret it was o