James McAvoy in Atonement Courtesy of Focus Features

"It is a romantic tragedy in every sense, but at the same time, it is definitely not sentimental," the actor says. "Instead of overly engaging your emotion, it endeavors to engage your intellect also. And [so] the actors couldn't go too far, I think. I could have gone much, much further, because I could believe in their love, and I could believe in his hate."

Robbie is sent with his British Expeditionary Force unit into France. But even in the face of the horror and carnage of war, his strength and nobility are tested and remain unshaken.

"He tries to not self-indulge," McAvoy says. "Even in the second half of the film, where he becomes a much more insular, self-interested person when he becomes so self-interested that if it weren't for Cecelia in his life reminding him of who he used to be, I think he would kill himself. He still tries to pull it right. He almost fails. But that is what you like to see, I think. We like to see people on the edge of damnation, of failure."

The director selected to helm this much-anticipated novel-to-film was Joe Wright, whose critically acclaimed first feature film, an adaptation of the classic Pride & Prejudice, featured a long tracking shot in the opening sequence. Once again, Wright opted to depict the army's retreat from and at Dunkirk as a single highly choreographed shot. This précis of the sorrow and the pity of war, says screenplay writer Christopher Hampton, was "a response to an economic constraint." The Dunkirk section of the book contains much more military action, with thousands of refugees streaming north, columns of soldiers being attacked by German bombers, and descriptions of sorties, side battles, and retreating armies. But with a cap on the film's budget, Wright decided to capture the horror of the Dunkirk aftermath on a single day's shooting. The beach was transformed into a macabre phantasmagorical Hieronymus Bosch scene that tracks Robbie as he and two of his comrades wander through the mayhem of the charred remains of a seaside resort where cavalrymen execute their horses, soldiers destroy their vehicles, and shell-shocked men sing hymns as a burning world descends into madness.

Keira Knightley and James McAvoy in Atonement Courtesy of Focus Features

"To choreograph," McAvoy recalls, "it took a couple of weeks to get it all set up. Joe probably took about two days with the main actors and the crew and then one film day with the one thousand extras in the scene. [But] he didn't panic. [Instead] he did something very bold and very brave and very audacious. He decided to rehearse all day and then shoot for an hour and a half, two hours at the end of the day. We got three and a half takes. Two and a half of them were rubbish and one of them was great. We didn't know that one of them was great because at the end of that day the monitor failed so we couldn't review our work." With a wry smile he notes: "So Joe was very tense. And as much as he tried to, he wasn't on good form that night."

McAvoy expresses much admiration for Wright, who, despite having now made only two feature films, has gained a reputation as being a "visual director." Being severely dyslexic, Wright left school with no qualifications, but managed to gain admission to art school based on the promise of his paintings and Super-8 films. McAvoy, however, feels that Wright's strength lies not only in his keen cinematic eye but also in his ability to impart a narrative.

"I always feel that Joe understands how to tell stories," McAvoy says. "He has more than one thing at his disposal with which to tell a story, and he realizes he can use all of them. And they are not just visual. They are not just audio. They are not just actors. It is not just set. There are a million things in a film he can use to tell a story. I think were he to do radio, I think he would make a success of it. Or were he to do mime, he would be able to tell stories well. It is not that he is a particularly fantastic mime artist it is because he understands what mime is there to do: to tell a story."