Cold Feet star James Nesbitt made a surprise appearance in the BBC's Line of Duty on Sunday night - and fans reckon it all points to one thing.
Actor Nesbitt's face loomed large on the computer screen of AC-12's detective Steve Arnott as he searched police files for clues to corruption.
It was explained that the character of retired copper Marcus Thurwell, played by Nesbitt, last known to be in Spain, had strong links to past corruption.
In particular links to CS Patrick Fairbank, who was unmasked as a seriously bad baddie back in series three.
Now fans of the hit BBC cop show reckon that such a high profile star as Nesbitt joining the action puts him in the frame as the infamous "H" - one of a group of corrupt coppers who have been leading the dodgy dealings throughout all six series of Line of Duty.
Mega-fans also pointed to the fact that the character of Thurlwell is currently hiding out in Spain - and in series five cyber crime specialist Amanda Yao had said that the IP address of "H" had been traced to Spain.
Meanwhile others drew possible links with AC-12 boss Ted Hastings who, like Nesbitt, is from Northern Ireland. He was seen looking wistfully at an old passing out photo as a young officer, which fans believe may also contain the character of Thurwell.
Viewers are now hoping that Nesbitt will feature more heavily in upcoming episodes.
And if he does, it will be something of a triumph for Nesbitt - who had only recently expressed dismay that he had never been asked to appear in the show by writer Jed Mercurio.
It also comes just weeks after thriller fans watched Nesbitt also unmasked as a corrupt cop in the BBC's Badlands - also penned by Mercurio.