Colin Firth, feeling 'Single'     The actor finds an emotionally rich role in the Tom Ford film

Colin Firth first came to international attention as Mr. Darcy, the thinking woman's sex object in "Pride & Prejudice," and then as Bridget Jones' slightly dazed consort, conspicuously named Mark Darcy. But the role of his life may be as George Falconer, the main character in Tom Ford's adaptation of the 1964 novel "A Single Man" by Christopher Isherwood.

Isherwood began the novel—considered the gay movement's first great work of literature—as a kind of thought experiment when his own longtime relationship with painter Don Bacardi seemed about to come apart. How, he wondered, could he cope with the loss of his life's love?

To work that out, he built "A Single Man" around the day middle-aged English academic Falconer receives the news of his own lover's death. The result was a novel—set in 1962 Los Angeles—of loss and love that speaks in universal terms.

Fashion designer Tom Ford read the book as a young man in the 1980s and was moved by its honesty and simplicity. When he read the book again three years ago, while searching for the right project for his first movie, the book struck him in a completely different way. It was a spiritual story, of sorts, about a man who could not see his future amid his isolation and crushing sorrow. Ford ultimately decided it would be his directorial debut. But where would he find his George?

It wasn't an easy question, since a cinematic treatment of "A Single Man" comes close to being a one-man play. He found his protagonist in an unlikely place: the London premiere last summer of the musical "Mamma Mia!"

Over lunch recently in Beverly Hills, Firth—one of the stars of the ABBA stage-to-film adaptation—said Ford sat in the row behind him and watched him carefully at a cast party afterward. A short time later, he received an e-mail from the fashion designer asking if he would consider playing the lead in "A Single Man." Firth, who at the time wasn't familiar with Isherwood beyond his book "The Berlin Stories," was intrigued. "I was impressed that Tom picked this material," Firth said, casually dressed after a long week of events promoting the movie, which opens in Los Angeles on Dec. 11. "It could not be dismissed as a fashion designer's vanity project. And even though I didn't know Tom at the time, I wouldn't have done that anyway."

Ford sent Firth the script, which he had written himself, and a copy of Isherwood's book. He pushed back the filming schedule to accommodate Firth, then paid the actor a personal visit, meeting him for dinner at the 1960s Bond-esque glamour restaurant Scott's in London.

"At first I wasn't sure if I could do anything special with the character George," Firth said. "But then, in many ways, George is consistent with what I normally do: He's a man around my age. He's English. He seems rather dry. He just happens to be in a state of despair for a very specific reason. He has lost someone, and he doesn't know how he'll live. He's feeling suffocated by life, and he's reached a point where he doesn't want to exist."

Like Ford, Firth came away feeling passion for the story and, specifically, for George.

"He's a man who really starts to understand the beauty of life at the moment he thinks he's letting go," Firth said.

Filming started almost immediately, at a Modernist home in Glendale that stood in for the light-splashed white cottage Isherwood and Bacardi shared in Santa Monica Canyon for so many years. "It came together very quickly," Firth said.

From the start, though, the actor knew that the biggest challenge in the film would be the scene in which he receives the news of his lover's death. It begins with a phone call—polite, almost clipped—and ends with a heart-wrenching portrait of emotional anguish.

"It's very difficult as an actor to begin a scene in one emotional state and end it in another," Firth said. "And since I had never worked with Tom before, I wasn't sure how things would be. The script wasn't specific. It was just 'phone call, dialogue, tears.' "

The actor quickly realized that Ford was trusting him to follow his instincts.

"There was a serenity on the set," Firth said. "I was given the space to engage and to feel it. Tom didn't bombard us with instructions; we weren't given any really. But you knew by the way he said, 'That was great,' if it was or wasn't great.

"He has this extraordinary talent for making his intentions your intentions, for making his vision your vision by just allowing people to be at their best. I don't think I'm any better or any worse than my material. Well, maybe I'm worse. I just played it as I saw it."

With complete quiet and few people on the set, Firth performed the phone call scene three times. Ford stood by, quietly. "He didn't cut the scene," Firth said. "He just let the [camera] magazine work its way out each time."

Actor and director also discovered they had something else in common: an interest in faces and the power of facial expressions on-screen. "To me, cinema at its most exciting is about the face," Firth said.

Since the movie began being shown at film festivals, Firth, 49, has been showered with acclaim. Although he has long been considered a fine actor, some critics believe his subtly powerful performance in "A Single Man" is his best yet. But to those curious about his decision to play a gay man, Firth has little patience:

"The movie is about isolation and the agony of loving someone who isn't there anymore," he said. "It's universal. It doesn't matter what your sexual [orientation] is. Love is love."