On June 10 1944, four days after the Allied invasion of Normandy, the inhabitants of a remote village in South-west France were rounded up by a company of SS soldiers and all but a handful were shot or burnt to death - 642 in total. The atrocity and its particularly disturbing details have never been adequately explained. In 1982, Robin Mackness met the one man left alive who held the knowledge which made sense of the massacre. It cost Mackness 21 months in prison. Convinced that he was not embarking on anything illegal, Mackness agreed to carry out an unusual task for a Swiss bank, of which he believed he was about to become a director. The task swiftly became a nightmare as he found himself falling foul of the French and Swiss law. He made the painful decision not to reveal the names of his banking colleagues or their client and was thereby sentenced by the French authorities who were deprived of an even bigger catch. In prison, Mackness began to research the background of the extraordinary story he had been told by the bank's client and five years of investigation convinced him that he had discovered the true secret of Oradour. His sources include members of the French Resistance as well as ex-members of the SS.