Today is the day Ivy Moxam escapes from the cellar, her prison for the last 13 years. After she makes a desperate 999 call from a phone box, Ivy is picked up by the police and taken to be interviewed. With no precedent to follow, DI Elliott Carne and DS Lisa Merchant question Ivy to see if she is who she claims to be while they wait for official DNA confirmation. But before they can confirm her identity, news of her escape is leaked and the police rush to contact the Moxam family before they hear it from the press. When the family is reunited, younger sister Emma is the only person with doubts; mother Christina and estranged father Angus need no proof that Ivy is their daughter. The police finally locate the house in which Ivy was held captive, but find her kidnapper long gone. Combing the house for clues, Merchant and Carne discover evidence that contradicts Ivy's story - and Merchant starts to question whether or not she's telling the truth.

Recent events put more pressure on Ivy to relive her ordeal and Carne and Merchant find themselves surrounded by a new team from Scotland Yard. Ivy is soon summoned back to the police station as Merchant comes up with a bold suggestion for jogging Ivy's memory, while White’s car is discovered abandoned. However, Ivy's behaviour makes Merchant suspicious, and when evidence is produced which suggests that Ivy has lied to the police, she comes under fierce scrutiny. She reaches out to Tim for support, but suffers a shattering betrayal.

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.

Ivy is arrested and questioned about the body discovered at Colbridge Road. She goes into shutdown and it's up to Christina to set Ivy free from the guilt that burdens her.

The Moxam family is plunged into the same horror they faced 13 years previously, leaving Ivy faced with the prospect of risking her own life to save Phoebe - and being confronted with the memory of her earlier ordeal. Carne and Merchant try to find a way to ensure her safety, but have underestimated Mark White, putting themselves in danger.