The fact that the abrupt, unexplained disappearance of one of its main characters might not be the most jarring plot turn in Olivier Assayas’ new film should tell you something about how peculiar and challenging it is. Not that “Clouds of Sils Maria” is unduly opaque either in technique or in narrative. But like the meteorological phenomenon of the title—a curious pattern of clouds near the Swiss town that joins with fog at certain times and sends the combination streaming between the peaks in a slithering motion resembling the movement of a serpent, which is therefore referred to as the Maloja Snake (Maloja being the district in which the town is located). The film takes a similarly serpentine route, playing with time, change and the proximity of fiction to reality in telling the story of aging actress Maria Enders (Juliette Binoche), who must confront the presence of death and the new place she has in her profession.

As she’s introduced, Maria is on her way by train to Zurich along with her personal assistant Valentine (Kristen Stewart) to participate in a tribute to writer Wilhelm Melchior, who gave her the co-lead in his play “Maloja Sils” when she was only eighteen and thus jump-started her career on stage and screen. She played Sigrid, a young, ambitious woman who takes advantage of the attraction that older woman Helen, a widow who’s taken over her husband’s business, feels for her, and ultimately drives Helen to suicide. Maria has been approached to revisit the play in a London staging overseen by a fantastically successful director, but this time playing Helen rather than Sigrid—something she’s very reluctant to do, especially since she’s currently involved in financially messy divorce proceedings. To make matters more unsettling, she receives information during the trip that Melchior has died, which will turn the tribute into a posthumous remembrance and add Henryk Wald (Hanns Zischler), her co-star in “Maloja Sils,” to the guest list—a fellow she despises as a man and an actor.

After soldiering through the event—and meeting with Klaus (Lars Eidinger), the director of the upcoming stage version of “Snake”—Maria agrees to take on the role of Helen, and she and Val repair to the remote house of the late playwright, whose wife Rosa (Angela Winkler) turns over the place to them to rehearse in after telling Maria the truth about Melchior’s death. There the two women run through the dialogue, often in a fashion that makes it difficult to tell where the lines of the play end and their actual conversation begins. They also go for walks in the mountains and dips in the lake, as well as excursions into town, where they drink heavily, go to casinos and manage to catch the new Hollywood sci-fi epic starring Jo-Ann Ellis (Chloe Grace Moretz), whom Klaus has in mind to play Sigrid. Jo-Ann has a reputation for Lindsay Lohan-like behavior, but Maria grudgingly admires her work even in drek (which the satirical clip we see from her picture certainly is), and agrees to do the play. And when Jo-Ann and her current beau, writer Christopher Giles (Johnny Flynn), visit the hotel near Sils to meet Maria, she turns out to be well-spoken and gracious, totally unlike her public image.

By the time the film reaches its epilogue in London, Valentine has been replaced with another assistant (Claire Tran) and rehearsals are about to begin. Unfortunately, the sailing is not smooth, not only because Jo-Ann has her own take on Sigrid, but because Giles’ wife, a famous artist, has decided to take that very moment to attempt suicide, sending the paparazzi into a frenzy around the young actress. Nonetheless the opening must go on, encasing both women in the setting of transparent boxes that Klaus has devised for their office scene.

This précis makes the film sound somewhat more conventional in presentation than it actually is. In addition to new footage of the Maloja Snake phenomenon, it also includes 1924 black-and-white shots of it—a juxtaposition that reemphasizes the script’s concern with past and present. Most of the scenes end in blackouts, fading to an empty screen seconds before one might expect and leaving the viewer in a state of suspense. The rehearsal sequences between Maria and Valentine jump between their conversations and the characters’, adding to the sense of disorientation. And the sequence of the two climbing to get a view of the clouds funneling down the valley of Sils Maria ends mysteriously.

Nonetheless the atmosphere of incompleteness and ambiguity is pleasurable rather than irritating, not only because of Assayas’ cunning script but because the performances are so incisive. One expects that of Binoche, who again seems to channel a real person rather than fashion a fictional one. And Moretz captures the air of a talented starlet whose offscreen antics might well be more calculated than they appear. But it’s Stewart who’s the real revelation here, showing a range that was imperceptible in the “Twilight” movies or any of the others she’s done, where she’s always seemed wan and bland. (A few mordant jokes refer slyly to the difference between those sorts of pictures and this one, and she seems to relish them.) The supporting cast is excellent as well, with Zischler standing out as the creepily self-promoting Wald, and Yorick Le Saux’s elegantly understated widescreen cinematography makes expert use of the locales. Even the eclectic music choices, which range from baroque to shrieking pop tunes, are apt commentary to the film’s themes.

Clearly “Clouds of Sils Maria” is not for fans of movies like the “Twilight” series, any more than David Cronenberg’s “Cosmopolis” or “Maps to the Stars,” both of which featured Stewart’s erstwhile love interest Robert Pattinson, are. But it’s a probing, illuminating rumination on art versus life, present versus past, and youth versus maturity, all craftily combined to invite reflection as well as admiration.