This is the story of Oleg Gordievsky, one of the West’s most valuable Cold War agents who risked everything to avert a third World War. Appearing to be an ambitious diplomat stationed at the Soviet embassy in Denmark. Gordievsky was actually a Russian spy and a rising star of the KGB. After a few years in Copenhagen, he was recruited by the British and posted to London by the KGB. Whilst in London, President Reagan authorised the largest NATO war game in its history: Able Archer.