The playwright Seán O’Casey grew up amidst appalling poverty in nineteenth-century Dublin. His father died when he was just six years old, and O’Casey then suffered from a chronic eye disease that made his school days a torment. Yet from those unpromising beginnings O’Casey went on to become one of the greatest dramatists of the twentieth century.There can be little doubt that O’Casey would scarcely have achieved such success without his older sister, Bella, a trained schoolteacher who helped the young boy to learn in spite of his grief and his eye troubles. Yet here is the mystery: when O’Casey later came to write his own autobiographies – in which he settles a number of old scores – he killed her off a decade before her time. Why?Mary Mor