'Billy Bob doused his sister with gasoline. Theresa Knorr waddled back to the car and started the engine. She watched as her son lit a match, dropped it on the bier and ran back to the car. If you ever tell anyone about this, you're goin' to be next, Theresa told her son.' To friends and neighbours, Theresa Knorr was a devoted, loving mother struggling to bring up five children on her own. Little did they know that, behind closed doors, the same woman was driven by religious extremism, terrible paranoia and an all-consuming jealousy of her daughters' beauty that led to one of the worst cases of serial abuse in history. For years, Theresa subjected her offspring to a barbaric variety of physical and mental torture, culminating in her ordering her two sons to drug, torture and then burn alive one of their sisters before starving another to death. Terrified that she would be next, a third sister had to take action. When the police found her story too far-fetched, she was left with no choice but to escape the house of horrors and fight for justice. It was years before the full, shocking truth came out. This is the true story of a family unit twisted out of all recognition by a mother who perpetrated the most evil of crimes.