THE TITLE of Olivier Assayas' latest refers to a beautiful, foreboding meteorological phenomenon that takes place in the Swiss Alps: With the right conditions in place, a bank of clouds will move away from a group of lakes, wending like a serpent through a mountain pass near the town of St. Moritz. It's stunning—but also an indicator of bad weather ahead.

This anomaly is also referenced in the title of a fictional play, Maloja Snake, which serves a key role in Clouds of Sils Maria. Maloja Snake was a drama that provided the first breakout role for now-beloved film actress Maria Enders (played by the always reliable Juliette Binoche), in which she played a young seductress who drove her employer and lover to suicide. Some 30 years later, Maria is asked to star in a revival of the play—this time as the seduced, emotionally tortured lover, opposite a diva-like film star (Chloë Grace Moretz).

Assayas plants this information about coming storms early in the film to add a peculiar, unshakeable note of dread that shades the interactions between Maria and her young assistant, Valentine (a startlingly great Kristen Stewart). In the film's best moments, the two act out scenes from the play together, with the lines between their own relationship and that of the characters they're playing getting blurrier all the time. The closer and closer they get to each other, the more worrisome their interactions become.

Clouds never turns in the directions you expect it to. Nor does it try to answer any of the questions it poses about the roots of Maria and Valentine's bond, or settle the film's ongoing debate about the state of the movie industry and celebrity. You're just left haunted and fascinated—and bracing yourself for a potential downpour.