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. What followed is a remarkable story of horror, love and the impossible survival of a father and his son. In this episode from the archive, Dan Snow and historian Jeremy Dronfield explore Gustav's secret diary, Fritz' accounts and other eyewitness testimony, and build a picture of this extraordinary father and son team.