When Czechoslovakia was liberated from the Nazis at the end of the Second World War, the population of the countrytook its revenge - not on the Nazis themselves, but on 3 million of their fellow citizens. Misha Glenny tells the story of this act of collective vengeance against the ethnic Germans of Czechoslovakia, and asks why European politicians of both left and right are still unwilling to acknowledge that an injustice was done. Producer Jolyon Jenkins