The French have nicknamed Audrey Tautou's new film "Amélie in the trenches", but in fact it could not be further from the last sweet, quirky soufflé concocted by director Jean-Pierre Jeunet. Instead, the star and director of Amélie have come together to make A Very Long Engagement: a three-handkerchief movie, with a vast American budget and a deeper, darker core.

Now, you might think the subject of love in the First World War has little left for the cinematic milking. But Jeunet's adaptation of the novel by Sébastien Japrisot illuminates - in glorious blue-grey and sepia - the hidden crevices of the war. The heroes are those at home, not at the front. The film follows the lives of five French deserters who literally shoot themselves in the feet, or the hands, and are tossed out into no-man's-land to die under a shower of German bullets. Of the wives and lovers back home, only the

fervent, forceful Mathilde, played by Tautou, believes that her young fiancé, Manech, is not dead. She begins searching for the truth, relying on detective work, instinct and superstition: "If I peel this apple without ever breaking the skin, Manech is alive," Mathilde says in one scene, a green ribbon unfurling under her knife.

"Amélie was a cartoon-style character; Mathilde is about

realism," says Tautou. In life, Tautou is a tiny, wide-eyed, delicate creature: it is hard to imagine her even having the strength to hold the bassoon that Mathilde sometimes plays in the film. Yet when she speaks she becomes more definitive. "I had to work harder as Mathilde, day after day, and it required endurance, not because of its complexity, but because of the pain involved."

Not Mathilde's corsets, surely, or the caliper she wears in the film, limping after a childhood bout of polio? "No," says Tautou, laughing. "The physical things were nothing. I got used to limping the first week. No, it was the continuing pain and sadness. There were no scenes that were a relief. I couldn't just relax and find

something funny, so I spent a month in that state, in that intensity, concentrating, so I could return to the character rapidly."

Indeed, during Warner Brothers' very long press-wooing for

A Very Long Engagement - the budget is an un-European £32 million and an unprecedented investment in something with subtitles - we visited one of the sets in the former government archives in Paris and saw for ourselves how Tautou remained resolutely in character between dozens of takes, as she stole records from the army files. Dressed in an exquisite long-skirted suit and lace-up heeled boots, there was no horsing around when the cameras were off. We knelt on the floor, ducking out of Tautou's eyeline, since gawking strangers, it was said, disturbed her equilibrium. One of the other actors added, "Audrey's very sensitive. Make a funny face before a take and she's in fits of laughter for ten minutes."

Tautou is 26, although she seems younger and somewhat unworldly. Her craft is mostly self-taught - she is puzzled by the mention of "method acting" and says she only attended drama school in Paris (where she now lives) for a short while. "People more experienced than me could go in and out of character," she says of this film, "but as Mathilde I could not. Plus, there was the inevitable loneliness of the film set, too far away from friends."

The daughter of a dentist, Tautou comes from Montluçon in the Auvergne. She first appeared on the scene when she won a César award for her portrayal of Marie in Tonie Marshall's Venus Beauty Institute (2000), and later she played a Turkish seamstress in Stephen Frears' Dirty Pretty Things. But it was her role as the eccentric Parisienne waitress in Amélie that provided her real breakthrough, when the film gained an international audience of 40 million. The combination of Jeunet and Tautou was clearly so bankable that Warner Bros is backing A Very Long Engagement as a Hollywood blockbuster in terms of promotion budget - batallions of journalists were brought on to at least three different sets in France, and the cast are going on a world tour. "The promotion," says Jeunet, looking

darkly resigned, "will go on for a year."

Explore Film

• Film Reviews

• Trailers

• DVD

• London Film Festival

Editor's choice

• The 100 Best Films of 2009
• The 100 Worst Movies of 2009
• The 100 Best Films of the Decade