Detective Sergeant Steve Arnott (Compston) is leader of a counter-terrorism unit that accidentally kills an unarmed man. Refusing to participate in a cover-up, Arnott transfers to an anti-corruption unit, AC-12, led by Northern Ireland veteran Superintendent Ted Hastings (Dunbar). AC-12 is in the process of investigating Detective Chief Inspector Tony Gates (James), who has just been awarded his regional force's Officer of the Year commendation. While Hastings is convinced that no one can be that good, Arnott initially questions the whole enterprise. When Arnott delves into Gates' case files, Gates is confident of seeing off the investigation.