The AC-12 team are back and there's a new, full Line of Duty trailer which implies the fourth 'H' could be a woman.
With heavy close-ups on Vicky McClure's Kate Fleming and Kelly McDonald's DCI Joanne Davidson, viewers are being kept on a string, with the show's makers teasing fans about the identity of the 'bent copper' at the heart of police corruption.
McClure, along with Adrian Dunbar and Martin Compston will return to Line of duty s eries six alongside Shalom Brune-Franklin, a new addition to the AC-12 team.
Trainspotting and Giri/Haji star Kelly Macdonald makes her debut as guest lead Detective Chief Inspector Joanne Davidson, the senior investigating officer on an unsolved murder case whose suspicious conduct attracts the attention of Anti-Corruption.
The action-packed trailer features armed units, an angry and disappointed looking Superintendent Ted Hastings and more finger-pointing than a game of Cluedo.
All the while investigations are uncovering police links with organised crime.
This is the sixth series of the phenomenally successful BBC show, which started on BBC Two in 2013.
The new series will be longer - seven episodes as opposed to the usual six - and will start on Sunday, March 21 at 9pm on BBC One.
