As a brutal stabbing leads DS Sarah Collins into the path of an undercover unit led by Kieran Shaw, Lizzie Adama is back at Farlow balancing her new role as DC with family life.

Sarah and Elaine are called to a brutal hit-and-run, uncovering a disturbing link to their ongoing investigation. Kieran urges Lizzie not to reveal the secrets of Operation Perseus.

Kieran and Bailie share information that could help Sarah secure an arrest, while Steve is under the spotlight when 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 confront Shakiel during a weapons handover.