'Appropriate Adult,' a British film airing Dec. 10 on Sundance Channel, is a fascinating and tremendously well-acted look into the heart of darkness. It features Dominic West and Emily Watson doing some of the best work of their careers, and it was well received when it aired in the U.K. earlier this year (the Guardian called it "mesmerizing").

But for a number of understandable reasons, West, who is best known for his leading roles in 'The Hour' and 'The Wire,' thought the role might capsize his career.

"It was something everybody advised me not to do -- certainly my wife didn't want me to do it," West said in a recent phone interview from his home in London. "It was not a popular decision in the press here until people had seen the film."

In 'Appropriate Adult,' the actor plays notorious serial killer Fred West, who, with his wife, Rosemary, murdered more than a dozen young women, including members of their own family, during the '60s and '70s. Many feared a film about Fred West would somehow glamorize the couple or otherwise minimize the damage they did to the victims and their families.

But West said the script by Neil McKay convinced him that the film offered him "a very well-written, very challenging role that I felt I couldn't give up even if it was to ruin my career, which I don't think it has yet." [See West's performance for yourself in the exclusive clip below.]