Detectives Sarah Collins and Steve Bradshaw investigate the deaths of the long-serving police officer Hadley Matthews and the 15-year-old Libyan refugee Farah Mehenni, who both fell from the roof of Portland Tower in south-east London.

Lizzie remains on the run; Sarah finally persuades her boss to go public about Lizzie's disappearance, and then makes a series of discoveries about the events that led up to the Portland Tower fall that further complicate the case.

Lizzie decides to turn herself in, but first she meets Kieran Shaw in secret, who tries to persuade her not to implicate herself; when Sarah finally interviews Lizzie, the explosive truth about the fatal night on the roof of the tower emerges.

Sarah investigates a cold case; Lizzie responds to a domestic violence call.

Sarah and Lizzie find themselves working on the same murder case.

As the manhunt closes in on Brannon, Sarah realizes where Tania's body might be buried.