The touch of skin, the sound of rain - the steamiest film of the year

If anyone else sat down in an interview and informed you "I wanted my film to feel like a caress", you might reckon they were being a bit precious. In the case of Franco-Vietnamese writer-director Tran Anh Hung however, the effect is decidedly disarming. Speaking French in a high and husky voice, he chooses his words with the sort of delicacy and precision you'd expect from the maker of The Scent of Green Papaya, 1993's exquisitely detailed memoir of colonial-era servitude.

"It had to have a gentle smile running through it, a sort of floating feeling," he says of his third and latest feature, which would sound terribly fey if the film hadn't turned out exactly as he describes.

At the Height of Summer is a contemporary story of desire and infidelity set in and inspired by the northern Vietnamese capital Hanoi. Shaped around the alternating romantic fortunes of three sisters – among them Tran Nu Yen Khe, the director's wife and ubiquitous leading lady – it pores languorously over the touch of skin on skin, the preparation of food, and the fall of the rain, its plangent visuals complemented by the Debussy-influenced reveries of Tran's regular composer, Ton That Tiet.

After the poise of Green Papaya, the expressionistic violence of Cyclo (Tran's Golden Lion-winning follow-up), it also shows a film-maker exploring new territory. Who could have expected the hang-loose sequences of brother and sister waking in the morning to the strains of Lou Reed and Scottish indie band Arab Strap, not to mention the film's discreet but palpable eroticism? Tran's one shot of two splayed, post-coital footprints halfway up a wall is sexier than all the exposed flesh in Intimacy.

The way the film-maker tells it, this is what happens to you when you visit Hanoi. He and his family hadn't lived in Vietnam since 1975, when they left for Paris before the fall of what was then Saigon. He's a French citizen now; he made Green Papaya in a studio in France, and only had his first experience shooting in Vietnam in 1994, when the renamed Ho Chi Minh City provided the backdrop for the demanding location work on Cyclo, the story of a young rickshaw driver caught up in the city's dangerous underworld. When production shut down for a Christmas break, Tran repaired to Hanoi. "I just remember seeing this young woman in the street in a beautiful light raincoat," recalls the 37-year-old. "There was such a gentleness about the place, a slowness almost to the point of immobility. "The problem then was how to find a style for the film which didn't just present the drama as a series of emotional problems for the various couples ... Somehow my thoughts turned back to my childhood in Danang, remembering the time when I'd be waiting to fall asleep at night, my mind racing from one thing to another, nothing precise. The smell of fruit coming in through the window, a woman's voice singing on the radio. Everything was so vague, it was like a feeling of suspension. If I've ever experienced harmony in my life it was then. It was just a matter of translating that rhythm and that musicality into the new film."

If this sounds rather more Proustian than our familiar images of war-torn Vietnam, then that's exactly the point. "I do get irritated by being this 'exotic' individual," he sighs. "Instead of looking at my films as works of art, they're seen as documents of everything Vietnamese. I'm always being asked about Vietnam, rather than the form or the style of my work or how it touches the viewer. I just tell them to go off and read some books. If my films are a document of anything, they're a document of my emotions about Vietnam. They're about expression rather than experience. They exist in the realm of pure emotion."

Ironically, they wouldn't exist at all if Tran hadn't grown up in France, been transfixed by the films of Robert Bresson, gone to film school, and developed the cinéaste's skills which transmute his half-oriental, half-occidental sensibility into the sort of ravishing form we see in At the Height of Summer. There's a character in the film, a botanical photographer, who has one family in Hanoi and, unbeknown to everyone else, a second family in a secluded lakeside spot where he travels to snap rare flowers.

"He's between two women, and that's me suspended between two countries. The sense he has of holding his breath all the time and not quite being able to live his life, that's my situation. I live in France, but part of me is always in Vietnam. Yet being this sort of nowhere man forces me to reflect, to question all the time. It's become very important, in a way. I feel uncomfortable, but lucid."

'At the Height of Summer' (PG) is released on Friday