It is best to just let yourself get lost in the "Clouds of Sils Maria" for a little while. Beautiful as they build then snake through the Engadin Valley in the Swiss Alps, they become maddening as they cloak the emotions and ambitions of a middle-aged actress and a rising young star.

In this richly imperfect piece about the vagaries to be found in a life spent working in film, French writer-director Olivier Assayas is most interested in the murky idea of returning — the ways in which humans circle back to the people they’ve been, the past they’ve had, no certainty about what might be discovered there.

‘CLOUDS OF SILS MARIA’ Rated: R Opens Friday at Kahala 8

That Assayas has chosen to do it with Juliette Binoche as his star represents a return to a creative collaboration the filmmaker and actress began three decades ago in "Rendez-vous."

It was a breakthrough for Binoche as an actress and for Assayas, who co-wrote the screenplay, as a filmmaker. "Rendez-vous" too was about stardom, though in that story Binoche plays the emerging ingenue. On many levels, "Sils" becomes a contemplation of much of what was then and a metaphor for what has happened in their careers since. Though they worked together a few years ago in 2008’s "Summer House," which was also about the passage of time, "Sils Maria" is a far more personal film.

Binoche plays acclaimed actress Maria Enders, not yet comfortable in the skin of the middle-aged woman she’s become. Kristen Stewart is her personal assistant Valentine, a smart, efficient, opinionated right hand who has become as much an artistic sounding board as scheduler of meetings. Chloe Grace Moretz enters a bit later as Jo-Ann Ellis, the rising star and an edgy, unruly favorite of the tabloid press. Her presence on a project that would remake the film that made Maria a star — with Jo-Ann stepping into Maria’s role and Maria taking on the older, desperate woman on the wane — sets the stage for a great deal of soul-searching about movies, the mainstream, artistic value and fame.

As the film opens, Valentine and Maria are on a train. Maria is to pick up a lifetime achievement award for reclusive playwright and filmmaker Wilhelm Melchoir, a Bergman-like character who, even if news of his death didn’t reach Maria in the first moments of the film, is far more potent as an unseen presence.

The jockeying for position that goes on after the great man’s demise uncovers wounds from an old, unresolved affair with another actor in ways that make Maria’s consideration of the remake, with Klaus Dieterweg (Lars Eidinger), a hot young director at the helm, more of a conundrum.

Through all of it, the relationship that captivates most is the one between Maria and Valentine. As stirring as Binoche is as Maria, Stewart is breathtaking as Valentine. Assayas uses the issues he parses in "Sils" to zero in on a personal-professional minefield that Stewart has navigated as well.

When Valentine tries to explain to Maria the relative value of the current blockbuster sci-fi film in which Jo-Ann stars, it is impossible not to think of the years Stewart spent on "Twilight" as Bella Swan, the role that served as a proving ground for the remarkable work the actress is doing now.

So affecting is Stewart’s performance in "Sils Maria," she became the first American actress to win a coveted Cesar award for it this year — France’s version of the Oscar.

In "Sils," Stewart does exactly what Valentine describes as Jo-Ann’s great gift — she becomes the character, completely disappearing inside Valentine. It makes the interplay between Binoche, a master of that sort of disappearing act as well, and Stewart mesmerizing to watch.

That interplay is the very heart of the film. The push and pull of their relationship, the co-dependence of a star and those close to her, comes alive as actress and assistant run lines, much of it as they hike the mountains around Sils Maria. With Yorick Le Saux as director of photography, the Alps provide a backdrop both stunning and physically challenging, which plays into the essence of what the actors are saying: Maria fighting the very idea of the older character every step along the way, Valentine arguing its relevance, its significance.

Assayas has many things to say about the contemporary dynamic of making movies and the easily manipulated egos and endless need for acceptance of its stars. There is a particularly telling scene late in the film. Maria, who’s been resisting the remake, agrees to meet with Jo-Ann. A polished young actress shows up, quite unlike the tabloid mess Maria’s caught on the Internet. Jo-Ann proves respectful, in awe of Maria’s work. Watching Binoche relax into the flattery is to be reminded of how remarkable she can be. Watching her brush it off when Valentine calls her on it later is reflective of a close but not always comfortable relationship.

"Sils Maria" was nominated for a Palme d’Or at Cannes last year. Some have suggested the director’s stinging candor about industry elitism may have cost the film the win. Perhaps, but I suspect the various loose ends he leaves and the occasional tabloid culture cliches that slip in had a part in its undoing. Still, the chance to look behind the curtain that Assayas has lifted so artfully is a temptation one shouldn’t resist.

In English and French with English subtitles.

Review by Betsy Sharkey, Los Angeles Times