The Tower

DS Sarah Collins and her colleague, DC Steve Bradshaw, officers in the Directorate of Special Investigations (DSI), are called to an incident at Portland Tower in south east London. They find at the bottom of the tower the dead bodies of long-serving police officer, PC Hadley Matthews, and a 15-year-old Libyan refugee, Farah Mehenni. Up on the roof Sarah finds a traumatised five-year-old boy and a rookie police officer, PC Lizzie Adama – 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, 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.

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

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

The hunt closes in on Brannon and Sarah narrows down the search for Tania's body.

The Brannon manhunt reaches its climax, and Sarah faces Tania's killer.

A stabbing leads DS Sarah Collins into the path of an undercover unit led by Kieran Shaw, and Lizzie Adama is back at Farlow balancing being a DC with family life.

Sarah uncovers a disturbing link in her ongoing investigation into working girl Lexi's death as Kieran urges Lizzie not to reveal the secrets of Operation Perseus.

Sarah's reluctance to cooperate leaves Kieran and Bailie exasperated, and Steve is under the spotlight as Shakiel puts his loyalty to the test.

The culmination of years of painstaking investigation and surveillance is upon Kieran, Steve and Operation Perseus as they prepare to for the final push.