A new series kicks off tonight of this crime thriller about a police anti-corruption unit. The opening episode sees a hardened criminal shot dead by an armed-response unit led by Sgt Danny Waldron, who claims they were acting in self-defence when interviewed by Hastings and Arnott. To find out more, DC Kate Fleming is sent undercover into Danny's team, and she is quick to identify tensions between the officers - only for her own conduct to come under scrutiny.