Detectives Sarah Collins and Steve Bradshaw are called to an incident at Portland Tower in London, where they find the bodies of a long-serving officer and a 15-year-old Libyan refugee. Up on the roof, Sarah finds a traumatized five-year-old boy and a rookie police officer - the only witnesses to what happened.

With Lizzie still on the run, Sarah finally persuades her boss, DCI Tim Bailie, to go public about Lizzie's disappearance. She then makes a series of discoveries about the events that led up to the Portland Tower fall, which 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 what really happened on top of the tower emerges.