Line of Duty

Sergeant Danny Waldron and his armed response team shoot dead a hardened criminal, but soon cracks appear in their story.

DC Kate Fleming uses her undercover role to increase the pressure on Danny Waldron's armed response unit; an old AC-12 investigation comes under legal scrutiny.

DS Steve Arnott believes Danny Waldron compiled a list of his childhood abusers; 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 a corrupt officer with links to organized crime.

AC-12's loyalties are divided when DS Steve Arnott is suspended from duty; with his career in jeopardy, Arnott turns to an unlikely source for help.

DS Steve Arnott is arrested on suspicion of murder.