Two years ago, I went to the concentration camp at Dachau, the pivotal location of this story. In an archive room, two German historians sat opposite me and told me that my grandfather would, without question, have known something about the atrocities that were taking place and that he would have socialised with some of the worst offenders of the Holocaust. Apparently I left the building, apparently I took notes in the doorway and my wife – seeing my face – took my photograph. I have no recollection.