DS Sarah Collins and her colleague, DC Steve Bradshaw, investigate the deaths of a long-serving police officer and a 15-year-old Libyan refugee.

With Lizzie still on the run, Sarah finally persuades her boss to go public about Lizzie’s disappearance, then makes a series of discoveries.

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 work together to hunt a killer. A new suspect emerges in the Tania case.

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

Lizzie and Brannon come face to face and Sarah finally tracks down Tania’s killer.

Sarah investigates the death of a teenage boy and comes into conflict with an undercover unit led by Kieran.

A brutal stabbing leads Sarah to unsettle an undercover unit led by Kieran Shaw.

Kieran and Bailie share information to help Sarah make an arrest while Shakiel tests Steve's loyalty.

The culmination of years of painstaking investigation is upon Kieran, Steve, and Operation Perseus.