A damaged ex-special forces soldier trapped in the criminal underworld is transformed into an avenging angel when an unexpected opportunity allows him to assume another identity. Once believing he was beyond redemption, he now seeks out his own version of justice.

Detective Chief Inspector Tony Gates is an exemplary cop. He's got the best crime stats on the force and a loyal team working under him. But the head of the police anticorruption unit, Superintendent Ted Hastings, has his doubts about Gates. Is he really that good? And more importantly, is he really that clean? Hastings decides to find out and all on a new arrival to his department, Detective Sergeant Steven Arnott to help him do it. As the net tightens...

The critically acclaimed drama returns for six more riveting episodes. In this season, DC Kate Fleming and DS Steve Arnott of AC-12 investigate the conduct of Sergeant Danny Waldron of the Armed Response Unit.