The last of five programmes
Presented by Rene Cutforth

The Lucy Ring was probably the most effective espionage network of the Second World War. It was Russian and it operated in Switzerland. Through this network Stalin was told the date of the German invasion of Russia -- but he didn't believe it. Only after Hitler invaded, on the day Lucy said he would, did Stalin take notice and fight the war largely on the contents of Lucy's messages. But who was Lucy? Where did the flow of incredible top-secret German information come from? And what were the coding techniques used by the Russians to keep their information secret?