TV producer Fliss Benson has been working on a documentary about miscarriages of justice involving cot-death mothers wrongly accused of murder. The documentary focuses on three women: Sarah Jaggard, Rachel Hines and Helen Yardley who have recently been freed from prison. Work is progressing well until Fliss receives an anonymous card at work. The card has sixteen numbers on it, arranged in four rows of four – numbers that mean nothing to her. Then Helen Yardley is found dead at her home, and in her pocket is a card with sixteen numbers on it, arranged in four rows of four…