Fanny Ardant plays Catherine, a middle-aged woman who’s heartbroken when she learns that her husband Bernard (Gérard Depardieu) is cheating on her. But instead of leaving him, she decides to get to the bottom of this infidelity thing. She goes to a sex club and picks out Marlène (Emmanuelle Béart), whom she renames Nathalie and pays to sleep with Bernard then come tell her everything in the most lurid details.

This simple but effective premise leads to a fascinating rapport between the two women. Ardant gives a complex, moving performance. Her character’s motivations are out there, but she makes up believe in them. Nearly the whole film lies in her reactions, in her very expressive face. Béart’s Béart, still the scrumptious sex doll at almost 40, but as usual she barely emotes. It’s all surface with her, like she’s always posing for a fashion photographer, but it actually fits the character here. She’s a whore selling a body, an image, keeping what’s inside deeply hidden. As for Depardieu… He’s good, I guess, but I’m getting tired of seeing him in every other French film (I’m starting to suspect that if you go to a website and enter your credit card number, he HAS to be in your movie).

Writer-director Anne Fontaine makes the daring decision never to show Bernard and Nathalie’s lovemaking, yet Marlène’s play-by-play and the way it affects Catherine is intensely erotic. The film is exquisitely well crafted, with an almost Kubrickian use of light and color (the film is more than a little thematically reminiscent of Eyes Wide Shut) and a lancinating quasi-Glass score by Michael Nyman.

Unfortunately, after a 4-star first hour, the story stops moving forward and the movie just spins its wheels for the remaining 45 minutes. We wait for the married couple to either make up or break up, for the two women to acknowledge the growing sexual tension between them and for the truth to come out, but no luck. Still, underwhelming ending and all, “Nathalie…” remains a powerful exploration of jealousy and desire.