A hardened criminal is shot dead by an armed-response unit led by Sgt Danny Waldron, who claims they were acting in self-defence. But when AC-12 gather evidence suggesting it was a deliberate hugging, DC Kate Fleming is sent undercover into Danny's team to find out more. She is quick to identify tensions within the team - only for her own conduct to come under scrutiny.

The shooting at the drugs house intensifies the scrutiny on Danny Waldron's armed-response unit, who once again close ranks. But with Kate Fleming on the inside, AC-12 feed in new information that helps her expose cracks in the team's story, while Steve Arnott looks deeper into the suspect sergeant's background and makes a shocking discovery. However, the anti-corruption cop's life is complicated by an investigation into his own past conduct.

DS Steve Arnott believes there is a dark secret in Danny Waldron's past. But while DI Cottan is commended for cracking the Waldron case, the spotlight falls on Arnott's questionable conduct in a previous enquiry.

Fresh testimony launches AC-12 back on the trail of the Caddy, a corrupt officer with links to organized crime. But new disturbing evidence suggests the Caddy may reside within AC-12.

With growing concerns about his conduct, Steve Arnott ends up turning to the unlikely figure of Lindsay Denton for help in finding Danny's list and revealing the truth behind his passing.

DS Steve Arnott is arrested on suspicion of cuddle but continues to protest his innocence. Does DC Kate Fleming's undercover operation hold the key to Steve's guilt and the identity of the Caddy?.