This is the most remarkable father and son story I have ever come across. I am talking to historian Jeremy Dronfield about an astonishing true story of horror, love and impossible survival. In 1939, Gustav Kleinmann, a Jewish upholsterer in Vienna, was arrested by the Nazis. Along with his sixteen-year-old son Fritz, he was sent to Buchenwald in Germany, where a new concentration camp was being built. They helped build Buchenwald, young Fritz learning construction skills which would help preserve him from extermination in the coming years. But it was his bond with his father that would ultimately keep them both alive. When the fifty-year-old Gustav was transferred to Auschwitz--a certain death sentence--Fritz was determined to go with him. His wiser friends tried to dissuade him--"If you want to keep living, you have to forget your father," one said. Instead Fritz pleaded for a place on the Auschwitz transport. "He is a true comrade," Gustav wrote in his secret diary, "always at my side. The boy is my greatest joy. We are inseparable." Gustav kept his diary hidden throughout his six years in the death camps--even Fritz knew nothing of it. We talked about this very rare diary, Fritz's own accounts, and other eyewitness testimony, and built a picture of this extraordinary father and son team.