Kristen Stewart has gotten a bum rap. She jump-started her career at the age of eighteen with a series of films that gave her nothing to do but be a sentient love-object to two equally dull men. Having made an obscene amount of money from this venture, she has since dabbled in the independent film scene, turning in one surprisingly excellent performance after another, the quality of the rest of the movie be damned (I'm looking at you, Still Alice). Now she's working with French auteur Olivier Assayas and has now won a Best Supporting Actress César for this film (the French equivalent of an Oscar). She's been a busy lady making up for all that lost time.

In Clouds of Sils Maria, there are vestiges of her airless work as Bella Swan. Here she plays Valentine, the put-upon yet devoted personal assistant to Maria Enders (Juliette Binoche). Her dark, lank hair is in a constant cascade around a pair of thick-framed, black glasses, contributing further to her project of self-effacement. She speaks quietly and conducts herself in a reserved manner, but is unafraid to stand up against Maria's more dramatic displays of selfishness. As the film goes on, we will question the exact nature of Valentine's feelings towards her boss, and whether they are merely platonic or something more.

Maria is a famous actress of screen and stage who is approached by a renowned theater director to act again in the play that granted her stardom. Rather than reprising her role as a beguiling 18-year-old, she will act the part of the spurned and ultimately rejected middle-aged lover, a reversal that burns the age-conscious actress to her core. Most of the film is spent watching her and Valentine rehearse scenes together, and therein lies the heart of the story. Given the clear age gap between Valentine and Maria (their actresses are 24 and 51, respectively), it becomes difficult to distinguish between real conversations and fictional ones. Through a combination of disarming editing and the performances by the women, Assayas blurs the line between truth and fiction until it just doesn't seem to matter all that much anymore.

This is not a Brechtian exercise, however. Assayas seems to be probing the depths of modern anxiety over irrelevance as well as the shifting landscape of what is considered "art." The young woman who has been chosen to replace Maria's original part is Jo-Ann Ellis (Chloë Grace-Moretz), an American superstar who has also encountered a bit of Lindsay Lohan-esque notoriety. The Internet-averse Maria initially learns about her co-star through an innocuous, flattering Google images search, only to learn from Valentine that the truth lies in the many YouTube videos of Jo-Ann violently fighting off paparazzi, getting arrested, and violating non-disclosure agreements on cable talk shows. Jo-Ann is very much intended to be the new thing in Hollywood, a gorgeous train wreck whom the public loves because of her imperfections. In contrast, we see the glamorous Maria posing with Chanel dresses and jewelry.

Valentine is the lynch-pin of the film, because she acts as a translator of the new world to the backward-looking Maria. Stewart's performance is an embodiment of that exceedingly difficult position, and she pulls it off with aplomb. Binoche is wonderful as ever as the mercurial, prickly actress who is still fully capable of turning on the charm when she needs to. Grace-Moretz is perhaps the weakest link in the film. She has much less screen time than her co-stars, and her initial impression is an uncomfortable one (see the aforementioned YouTube videos). We also see her in a dopey sci-fi action movie that Valentine allegedly loves, an idea that I cannot for the life of me imagine. At only 18, she is still a much less experienced actress than the other two. She doesn't completely lose her presence when she shares the screen with them, and shows a capacity for true cruelty towards the end of the film. She just doesn't quite have the chops, yet.

Underpinning the film is a sense of unease, something that is initially manufactured by the constant buzzing of cell phones (Valentine wields both an iPhone and Blackberry to do her job) but then moves into the more ethereal, yet still somehow menacing clouds of the title. These clouds refer to the natural phenomenon that occurs in the Swiss alps where the film is mostly set, in which a thin stream of clouds will snake its way through the valleys between the mountains. It is a brilliant, haunting image to which Assayas returns repeatedly throughout the film. Scenes are book-ended by images of the mountains, enormous, white, and imposing. The small story of these women is dwarfed by nature, reminding me initially of Michelangelo Antonioni's L'avventura. That film will come rushing to mind again later on, for reasons I won't spoil.

Assayas has created an enigmatic, elliptical work of art with Clouds of Sils Maria. He derives career-best performances from his actresses, even if the youngest may falter a bit in comparison. It is gorgeously shot (in 35mm, courtesy of funding by Chanel), tightly written, and very much for adults. It's even mostly in English, which is a plus for all you foreign language film haters out there. Don't let its ponderous title fool you: this is about as gripping as a film about women having conversations gets.