In the film, Balibar and Amalric play a couple negotiating the breakdown of their relationship and the death of a mutual friend. In life, they are married and, when I met them in Paris, were about to take off on holiday with their two children.
The couple first acted together in Arnaud Desplechin's 1997 film My Sex Life (How I Got into an Argument). Immediately they became the two principal faces of what is referred to, somewhat amorphously, as "the Young French cinema". Amalric plays Paul, a boyishly likeable if infuriating presence, a Jean-Pierre Leaud for the 1990s. And Balibar was electrifying as Valerie - a she-devil philosophy student who enchants Paul, then utterly terrifies him with her unpredictable behaviour.
Though Balibar was plausible as a contemporary character, there was a quality about her as an actress that could belong to the French cinema of the 1930s and 1940s. "I'm constantly being told that," she laughs. "It's getting a bit tiresome, having this air of anachronism." She can change from interrogatory silences - holding her partner with luminous, piercing eyes - to skittish action, emphasised by her expressive angularity. But it was mostly in the quality of her voice, which is able to skip across several pitches in the space of a line and to suggest a cajoling, curious intelligence that was never very far from the comic.
This unpredictability is well to the fore in Late August, Early September. The film opens on a scene in which she and Gabriel, her ex-partner - played by Amalric - are showing prospective buyers around their flat. Gabriel keeps up the salesman patter, leading the other couple from room to room. Balibar does little other than hug the wall, her face switching and twitching. The dismantling of what was once their shared domestic space hurts her. And she shows this without saying a word. "Jeanne is a changeling in front of the camera," Amalric says. "You never know quite how far she'll go."
Late August, Early September is an anatomisation of emotions, reminiscent of older directors such as Claude Sautet and Andre Techine; and that's part of its interest. When films like Sautet's A Heart in Winter or Nelly and Mr Arnaud reached our shores, they did so partly on the star-power of Emmanuelle Beart. But they were also attempts to find a younger audience for this sort of cinema. Late August continues this tradition, but with a stylistic lightness that will be familiar to those who saw Assayas's Irma Vep - his sixth feature but the first to get a release in the UK. It was a cult success, a kind of loose-limbed remake of Truffaut's Day for Night with the Hong Kong action-movie starlet Maggie Cheung essaying the part of the French silent cinema icon Musidora.
Carrying over the hand-held camerawork of Denis Lenoir, the cinematographer with whom Assayas has shot all of his features, the style of Irma has been brought to bear on Late August, a story whose concerns - friendship and work, love and death - are treated in a fragmented narrative. Gabriel's friend, a writer named Adrien Wilier (Francois Cluzet) dies and the repercussions are felt by his circle of friends. We don't see the physical death. Instead, Assayas chooses to show the emotional impacts and consequences that Adrien's social death has on a terrific ensemble cast, which includes Francois Cluzet and Virginie Ledoyen, who's soon to appear opposite Leonardo Di Caprio in The Beach.
Balibar's particular place in French cinema is as the embodiment of cultured, middle-class, and frequently Parisian femininity. There's little doubt that she could play the glamorous costume-drama queen or even take the route to being an international token of class, a la Juliette Binoche or Irene Jacob. But for the time being her chosen place is in the low- budget end of auteur cinema - which brings us back to the accusation of "navel- gazing". Balibar has no time for it. "You know, this sort of cinema is often seen as being about sons from good families with existential problems and, while I don't want to come across as paranoid about these things, that attitude is part of the war between a very commercial, Americanised cinema and an auteur cinema in France. The films of directors such as Assayas and Desplechin are part of a cinema of resistance, one that resists the heavy artillery of big-budget movies by talking about things that are delicate, subtle and literary. It's a cinema that's more on the side of art than spectacle and that has more to do with details than special effects."
Balibar's own background is comfortably part of this milieu. The daughter of the French philosopher Etienne Balibar, she was bound for an academic career from an early age and lived in England for two years while doing research in 17th-century English history at Oxford and Cambridge. But when she returned to France, a spell at the Conservatoire in Paris put a stop to her studies.
Her partnership with Amalric has seen them cast together recently in another low-budget feature, Three Rivers, directed by Jean-Claude Biette.
Amalric himself, whom Assayas describes as "the essence of contemporaneity", has been around film-making since the age of 17, when he lived in Moscow with his journalist parents and was cast in a film by the Georgian director Otar Ioselliani. "I wanted to do what the director was doing," he recalls. He has since made several shorts and is preparing his first feature, in which he will direct Balibar. It's an adaptation of an Italian novel called Wimbledon Stadium. They're due to shoot in south London next autumn. But a lot could happen in these careers between now and then: "the faces of the new French cinema" have scarcely begun.
`Late August, Early September' (15) opens on 20 August