Colin Firth has been wandering around London looking dazed, confused and dishevelled. The reason? The Bridget Jones' Diary star has gone back to his roots, before playing Darcy in Pride and Prejudice turned him into a global sex symbol and recast his screen persona as a romantic lead. The forthright Firth plays the psychologically distraught Ben in Marc (My Little Eye) Evans' horror thriller Trauma, the first in a series from Little Bird's 'Ministry of Fear' genre label.

Ben awakens from a coma to discover his wife has been killed in a car accident and, after being haunted by ghostly visions, loses his tenuous grip on reality to enter a vortex of hallucinatory confusion. Can his enigmatic neighbour (American Beauty's Mena Suvari) help separate fact from fiction in his tortured mind? Firth revealed, "Trauma may seem a departure from what I'm now known for but I was appearing in quirky features like Tumbledown about the horrors of war, and Apartment Zero about the human psyche's dark side way before I took on Darcy. Ben is the sort of role that was my territory in the early days. Marc and I worked together on the Ruth Rendell TV movie Master of the Moor and I thought he was brilliant. So I wanted to join him again but our numerous attempts never quite panned out. Then Trauma came out of leftfield and intrigued me enough to sign on to what was clearly going to be an interesting journey. My main motivation for doing anything these days is to work with people I have always wanted to collaborate with and this seemed the perfect opportunity for us. It's a hard film to discuss because not only is the entire film told from a subjective point of view, meaning I'm in every scene except for the final shock revelation, we must also strike a balance between being overly obtuse and cryptic to being boringly prosaic and explanatory. We don't want to frustrate the audience by being too baffling about what's really going on but we still have to retain the necessary air of mystery.

Marc is not shy of the generic aspects of Trauma and his main inspirations come from Krzysztof Kieslowski's Three Colors: Red, White and Blue, Nic Roeg's Don't Look Now and Roman Polanski's Repulsion and The Tenant. That gives you a rough idea of the twisted psychological zone we're in. Trauma's horror is organic and even scarier than usual because it's based around the door to the subconscious mind that should be shut but has suddenly become slightly ajar with terrifying ramifications."

Firth will be back on screen soon in Peter Webber's Girl with a Pearl Earring as 17th Century Dutch painter Vermeer in the suspenseful story behind one of the master's greatest and most enigmatic portraits. As Trauma wrapped, he was readying himself for the Bridget Jones' Diary sequel, The Edge of Reason. "Yes, I'm in the sequel and I don't mind at all because the original was an enjoyable experience. It was a blessed relief to be in Trauma because it couldn't be further away from that type of romantic comedy. I don't want to stay out of that popular genre forever, but it's gratifying to know some people realize my range is still broad. Ben wasn't familiar to any character I've done before. People won't be expecting this grief stricken strange person from me and that's why I simply had to do it."

Trauma will be released early next year.