WATCH: Line of Duty Season 6 trailer hints at a big reveal for the show

Mother of God.

A new trailer for Line of Duty Season 6 has been unveiled and hints towards a massive revelation for the hit show. The action packed teaser - featuring shootouts and car crashes - reveals the upcoming season will see anti-corruption police unit AC-12 looking into a murder that is their "highest profile investigation" yet. The unit want to know if police corruption is why the murder has remained unsolved. However, the closing moments of the clip are the most important. Previous seasons of Line of Duty have established there is a group of senior ranking corrupt police officers who wield considerable influence. Much speculation surrounds the identity of these officers and over the course of the show three have been identified with a fourth still unknown. The new trailer ends with Martin Compton's DS Steve Arnott being asked if he still believes there's a fourth man out there. He replies: "Man or woman?" before viewers see a shot of Vicky McClure's DI Kate Fleming. Is Fleming a bent copper? If so, it would be a major twist given she has been part of AC-12 since the show began. Thankfully, viewers won't have to wait long to find out as BBC One have confirmed Season 6's first episode will air on 21 March. The network have also confirmed that Line of Duty will be returning for season 6 with an extra episode. This series will feature seven episodes, as opposed to the regular run of six. Check out the trailer for Season 6 below. We know you didn't float up the Lagan in a bubble, but do you think you can get top marks in this Line of Duty quiz? Clip via BBC.