As the police start to make breakthroughs in their investigation, Ivy turns to her sister Emma, who seizes the chance to connect with her. But they are interrupted by the arrival of a mysterious letter addressed to 'Alison' - White’s name for Ivy. DI Carne reaches out to Ivy, desperate to find a window into Ivy’s mind, but when she refuses to cooperate he is forced to take drastic measures in search of the truth. Meanwhile, with doubts building over Ivy’s story, DS Merchant returns to Mark White's house and makes a shocking discovery.