This film tells the story of the extraordinary risks MI6 and the CIA were willing to go take to get vital intelligence during the Cold War. It’s 1954, the height of the Cold War. As the arms race builds to a fevered pace, spymasters in Britain and America know they have to find a way of infiltrating the Soviet machine. They must find out what Russian intentions are. This is the gripping true story of Operation Gold: the mission to build a 450-metre spy tunnel under Berlin, one of the most heavily guarded cities in history.