Helen Duncan - known since childhood as 'Hellish Nell', for her uncontainable nature - was one of the most popular mediums of the twentieth century, holding seances around the country where she was believed to manifest the spirits of the dead. What happens when we die? It was the question of the age for a generation which had endured one world war and now was living through another. Mrs Duncan's seances offered an answer. But when she started foretelling naval disasters, she also attracted the unwelcome attention of the secret service. And so just weeks before the Normandy landings, absurdly, anachronistically, she was prosecuted for witchcraft and jailed. Was Nell a conjurer, a martyr or a security risk?