Sarah* was, in many ways, the archetypal lost sheep. Brought up by poor immigrant parents, battered by her father as a girl, she never seemed to have a chance. For years we hardly saw her, hidden, as it were, in a back room by her widowed mother. She was on drugs: heroin, cannabis, anything she could lay her hands on. Then in her thirties she vanished for a long stretch inside one of Her Majesty’s Prisons. She returned more sinister than before, dragging an air of …