L'affaire Jack King 2015

Between 1940 and 1945, an MI5 agent going by the name of Jack King infiltrated Fascist networks in Great Britain by posing as an undercover Gestapo officer. His main mission was to intercept strategic documents stolen by pro-Nazi sympathizers. How was this operation organized? What role did the British secret service play during the war?And who exactly was the man behind the code name Jack King?