Agent Jack: The True Story of MI5's Secret Nazi Hunter (2018)

This is the incredible tale of Operation Fifth Column, a Second World War MI5 operation so secret that its existence was only revealed by the National Archives for the first time in 2014. Throughout the war and even for a couple of years afterwards, 'Agent Jack' - in reality, a bank clerk named Eric Roberts - acted as a Gestapo agent to whom hundreds of British-based Nazi sympathisers and informers passed their secrets, thinking that he was sending them back to Germany. Many were put on a salary by what they thought was the Third Reich and some were even 'awarded' Iron Crosses for their services to the Fatherland; they never found out the truth.