Juliette Binoche and Vincent Lindon portray a couple whose relationship is tested with the arrival of an old friend that is also an ex-lover in Claire Denis' latest movie.

The premise of "Both Sides of the Blade," which premiered at the Berlin Film Festival on Saturday, may not be entirely original, but for director Denis, her film is distinguished by its adult, unflinching approach to a menage-a-trois and a refusal to apportion blame.

"That was the film's angle," she told a news conference. "We weren't going to judge them. We weren't going to reject them. We were with them."

Binoche plays Sara, an accomplished radio journalist whose life with retired rugby player Jean (Lindon) is complete. While she interviews the world's oppressed for her show, he potters happily and does the shopping.

In the evenings they return to their beloved flat on Paris's Rue d'Amsterdam, a welcoming space that suddenly turns close and oppressive when Francois (Gregoire Colin) reappears in their lives.

As sly and intriguing as Jean is open and gentle, Francois is Sara's former lover, and the two men are also former friends and business partners. Soon, the protagonists start leaving the room to take hushed phone calls.

Denis said filming this part of the film took a psychological toll, the crew shattered after filming Sara and Jean's final row.

But, according to Binoche, it is crucial not to cast that sudden change as a failure of the marriage. Rather, she said, the film says this needs to be acknowledged as a reality.

"You're obsessed by him, by this person, you are your needs of having him inside you as a woman, it becomes like a need that is so big," she said. "There's nothing psychological about it. It's visceral."