'Line of Duty' is set to return for a seventh series.
The BBC police thriller could be back as early as next Christmas, with Martin Compston, 38, Vicky McClure, 39, and Adrian Dunbar, 64, all said to be on board to return for a new three-part series.
A TV insider said: "There was a very strong feeling, particularly among fans, that there was unfinished business with 'Line of Duty'."
Series six of the hit show - which is written and created by Jed Mercurio - saw elusive criminal mastermind H finally unmasked as bumbling Detective Superintendent Ian Buckells (Nigel Boyle), but some fans believe there could still be a "darker puppet-master" at work.
The insider added to The Sun newspaper's TV Biz column: "Viewers weren’t satisfied with the ending of series six and were crying out for a more sensational conclusion - now Jed can deliver that.
"The question is whether the person we were led to believe was H really is the villain that AC-12 has been hunting or if it was another nemesis.
"There’s also a theory another, darker puppet-master is at work.
"The fact that they’re looking at taking the unusual step of making three episodes rather than the usual six or seven is a reflection of just how special this is for the show."
Just this week, Vicky - who portrays DI Kate Fleming - admitted she was "sure" 'Line of Duty' will return at some point.
She said: "I speak to the lads all the time, we'd all love to, we're all game - Martin's in nine shows!
"It's busy, I'm sure we'll get there."
Last month, Adrian - who portrays Superintendent Ted Hastings in the hit police drama - admitted the 'Line of Duty' cast have been "keeping their fingers crossed" that there will be a seventh series.
Asked if they might "do another one", he replied: "Yes, there is every possibility. We're all keeping our fingers crossed that we'll hear something at some point.
"We all want to get back together again. We'd love to go back to Belfast again."
In August, Adrian admitted a new 'Line of Duty' series might focus on "something from past episodes", and he teased that the 2021 finale - which drew in almost 17 million viewers - may "not be the last" audiences see of the BBC show.
He said: "My thinking is that, no, it's not the last you might see of us. I know that there are people who are talking and some plans, but I don't know exactly what would happen. I don't know what shape it might take. There was talk of a film, there was talk about maybe two 90 minutes, there was talk about three one hours, I don't know."
The BBC have declined to comment.