The hasty Belfast reshoot that will ensure Line Of Duty ends on a high
It's a crime series finale that will have millions of viewers gripped.
When the creator of BBC2 thriller Line Of Duty decided to rewrite the ending, he hoped the actor involved was still in Belfast, where the drama was filmed.
After watching footage, writer Jed Mercurio felt that something important was missing from the denouement and that the hugely-anticipated ending did not work as well as originally thought.
So Mercurio rang the actor to say he or she would have to re-shoot – and struck lucky.
He told The Observer: "Luckily, they had not flown out yet. So we grabbed them and quickly filmed another sequence, which was then edited seamlessly into a scene."
The writer does not reveal the actor's gender deliberately to keep the audience in suspense. Since the second series began airing on BBC2 last month, more than three million viewers have tuned in to try and work out which cop is corrupt – DI Lindsay Denton, played by Keeley Hawes, or Mark Bonnar's DCC Dryden.
Due to the high level of interest in the show, its makers, World Productions, decided not to run trailers for the following week after each episode, as they gave too much away.
Mercurio said: "It is fantastic that so many people are talking about it, trying to work out whether Keeley Hawes's DI Denton is guilty."
When the actors were given the scripts they were kept in the dark as to who was guilty, only finding out before shooting began.
The first series of Line Of Duty, which aired in 2012 and was filmed in Birmingham, centred on an anti-corruption investigation into DCI Tony Gates, played by Lennie James. When it was revealed James would not be returning for series two, some viewers speculated that the show would not survive without him.
But critics have praised series two as stronger. It is hoped a third series will be recommissioned after Wednesday night's finale.
Mercurio told the Belfast Telegraph last month: "For legal reasons the BBC did not want us to set the drama in a specific city because it deals with the sensitive issue of police corruption.
"In terms of locations, local cast and crew, we had a great experience shooting in Belfast. It doubled seamlessly for our anonymous English city."
The actors also want to return to Belfast. Martin Compston, who plays DS Steve Arnott, said that while relocating to Belfast had been tough to begin with, "it was a great set and if we do come back, I'll look forward to it".
Hawes said: "I loved filming in Belfast. The Northern Irish were really welcoming and one of the nicest crews I have worked with."
Line Of Duty and Belfast-based drama The Fall, currently filming in the city, have given BBC2 two of its most successful dramas in recent years. Twitter has been buzzing over the last few weeks with various theories about the identity of the corrupt cop, while there is much excitement about the return of The Fall later this year. Local broadcaster Colin Murray tweeted: "Football over...time for #LineofDuty ep1, series2, freshly recorded and unmissable", while Northern Ireland Screen posted: "Is there anything good on TV these days not made in NI or by an NI company @Line_of_Duty?"