A new Line of Duty trailer was shown after the dramatic finale of BBC series Bodyguard on Sunday night.
The teaser clip of series five showed the return of AC-12, with some viewers claiming it was more exciting than the last episode of the political thriller.
Superindent Ted Hastings (Adrian Dunbar) is seen looking unhappy as he discussed the team's next challenge in Jed Mercurio's critically acclaimed crime drama.
"AC-12 is being met with an institutional cover-up," he says. "We'll get to the root of it."
Detective Sergeant Kate Fleming (Vicky McClure), then asks: "The root being what, sir?"
Fans were arguably most shocked by the appearance of Detective Sergeant Steve Arnott, who appeared sporting some new facial hair. His beard made him look noticeably different to the clean-shaven character fans have been familiar with since season one.
DS Arnott is seen running to a house with a children's slide in the garden as sirens wail in the background.
Actor Martin Compston, who plays DS Arnott, tweeted: "Sneakiest of sneak peaks of @Line_of_Duty there but we're back fully loaded and bearded."
Series five of Line of Duty returns to BBC One in 2019
