The actor, who played DI Matthew ‘Dot’ Cottan in the first three series of the hit BBC cop show, has said that the episode will “shock people”.
Craig hosts the BBC’s Obsessed With Line Of Duty podcast and made an appearance on Dermot O’Leary’s Radio 2 show on Saturday to discuss the finale.
He said: “I think it’s gonna shock people. I think people are going to be frustrated, it’s exhilarating, it’s exciting… these aren’t soundbites, I’ve seen it four times, honestly, and it really stands up to repeat viewing.”
While he’s already seen the episode a number of times, Craig refused to be drawn on spoilers when Dermot presented him with a number of fan theories.
When the presenter said he would be devastated if Superintendent Ted Hastings turns out to be “the fourth man”, Craig said: “You know I can’t answer that.”
Asked if AC-12′s DC Chloe Bishop might be the daughter of series one’s DCI Tony Gates, he said: “Don’t go there.”
He added of his own theories: “I’ve been prone to a lot of overthinking, because a lot of my theories from episode to episode have been so wrong and so ridiculous.”
Craig was also asked if he believes the show will return for a seventh series, to which he said: “We’re so emotionally invested in the show and certainly the main trio, I would love it to come back, I think everyone would love it to come back.
“But you have to know when it’s a good time to get out and walk away with pride and dignity.”
Earlier this week, Craig predicted Hastings could be about to exit the show.
Speaking on his podcast following Sunday’s penultimate episode, he said: “With those images of what Ted’s been reduced to, and physically and mentally where he is, yes, I do believe he’s going to exit the show and he deserves nothing but a hero’s exit.”
A trailer for Sunday’s series finale has promised viewers that the identity of ‘the fourth man’ – otherwise known as ‘H’ – will be revealed.
Hastings is among the suspects, along with Carmichael, Osborne, DI Kate Fleming and ex-officer Marcus Thurwell.
It also previews other dramatic events in store, including another armed face-off AC-12 have with members of the OCG as they look to secure the suspect, while DCI Jo Davidson also faces an uncertain future, following her imprisonment.
The internet is already flooded with theories ahead of the finale, as many fans believe Marcus Thurwell is actually alive, after the character was found dead at his Spanish villa – and some of then claim to have the proof.
Suspicions have also been raised about DCS Carmichael, as some viewers spotted what they believe might be a clue that confirms she’s ‘H’.
Line Of Duty concludes on Sunday at 9pm on BBC One. The Obsessed With Line Of Duty podcast is available to stream now on BBC Sounds.