By Caroline Briggs
BBC Entertainment reporter
Colin Firth stars alongside Kevin Bacon in the film
Colin Firth's new role in Where the Truth Lies will come as a surprise to fans used to seeing the actor in more romantic roles.
His roles in the two Bridget Jones films, the Brit-flick Love Actually, and his breakthrough role as the smouldering Mr Darcy in the BBC's Pride and Prejudice, has ensured him a legion of female fans.
But Where the Truth Lies, by director Atom Egoyan, sees Firth cast in a much darker character alongside Hollywood star Kevin Bacon.
They play Vince Collins (Firth) and Lenny Morris (Bacon) - a comedy duo who are the darlings of 1950s America.
But their reputations are sullied when a young woman is found dead in their hotel bath tub and, despite water-tight alibis, their partnership is over.
Neither speaks to the other, or to anyone else, about the death until the 1970's, when ambitious writer Karen O'Connor (Alison Lohman) begins to look into it.
The film explores the dark side of fame, fortune, and celebrity, something Firth says he was immediately attracted to.
"I liked all the dark stuff, the unpredictability of the character, and I thought it had a lot of possibilities," he told the BBC News website.
"[Darker roles] are not entirely new to me. In Trauma, which I did about three years ago, and throughout the 1980s, I was playing characters who were less than pleasant.
"It's not a reaction to typecasting - I just tend to like that territory.
"I have reaped enormous benefits from doing rom coms... but I tend to be more comfortable in drama than in comedy."
While Firth admits he would be open to future comedy roles, there is the possibility of more gritty roles in the near future.
"Tortured is always good for an actor. I don't know anyone who doesn't want to do a bit of torturing," he added.
"It is hard to imagine any central character in any film that is happy at the beginning, happy in the middle, then happy at the end. What story has there been?"
Firth is famous for his role as Mr Darcy in the BBC's Pride and Prejudice
But while Vince may be a polar opposite of Darcy, there was one element of his affable Englishman demeanour that Egoyan was keen to tap into.
"Vince was originally an Italian-American, but that was never going to happen," said Firth.
"[Atom] thought it would be more interesting to use what people associated with me already and he was absolutely right.
"There is something that surprises people more about the character if I play this buttoned-up Brit who goes off stage and beats the crap out of people and behaves in an evil manner."
While the violence is graphic, it is the explicit sex scenes - one in particular - that caused controversy in the US.
It was released with a restricted NC-17 by the Motion Picture Association of America, despite Egoyan's cuts to the contentious scene.
He later failed in a bid to challenge its rating.
When asked about the controversy Firth throws his hands up in defeat.
"In terms of the psychology of the film [the scene] is critical. If that scene was not critical we would have saved ourselves a lot of grief at the box office by chopping it out, but you can't.
"It's not the most explicit scene I have ever seen, there is not full-frontal nudity, so it's not that.
"I can only think that because the scene itself is uncomfortable - and intentionally uncomfortable - that they were reacting to that discomfort and considering it across whatever threshold they are using to judge."
Firth is succinct about the perils of taking his clothes off for a living.
One sex scene caused particular problems with censors
"It's a bit grisly at first really, but it's alright," he laughs
"You've got the added obstacle of cameramen going into contortions trying to frame out your privates at the same time.
"In a film situation you are asked to do all kinds of things that are not usual: you pretend to kill people, torture people, conjure up rage which would be completely anti-social in any other situation, and so the sexual thing is only one more weird thing we have to do."
Firth admitted the role also provided an uncomfortable glimpse into the future of a celebrity whose fame turns sour.
"Vince is a very, very bleak character to portray in that way and playing him was a real stare into the abyss. There but for the grace of God go I.
"It's a horrible glimpse at what happens when you walk out of the limelight and into total isolation, and I think it is a very, very easy thing to happen.
"If you invest in that sort of adoration and you capitalise on all those perks, it is going to distance you from real human beings and real relationships and Vince is totally dysfunctional in that way.
"It's also the fear of mediocrity and spinning into that place where over years and years the quality of your work just declines, declines until people who used to celebrate you now feel a bit sorry for you.
"I don't want to think about it at all. You've depressed me terribly," he joked.