Are English-speaking directors stupid? It may be an impertinent question, but it seems a necessary one in a year when chronically underutilized Kristin Scott Thomas has essentially reinvented herself as a French actress, first with a small role in Guillaume Canet's evocative thriller Tell No One and now, as the mesmerizing lead of Philippe Claudel's I've Loved You So Long.

Like another compelling fall drama, Jonathan Demme's Rachel Getting Married, Claudel's film is about the return of a sister, a sister who has done a terrible thing, a sister who has spent time institutionalized and must learn to reintegrate herself into family--and civilized--life. The similarity ends there, however. Where Demme's protagonist (played by Anne Hathaway) expressed her damaged self by acting out flamboyantly, Scott Thomas faces the still more difficult challenge of turning inward, of conveying the fierce, wounded spirit buried beneath so many layers of grief and hopelessness that it has almost been extinguished altogether.

We first meet Juliette Fontaine (an almost unrecognizably unglamorous Scott Thomas) waiting at an airport, smoking a cigarette as if she half hopes it will kill her. Her face, devoid of makeup, looks as worn and faded as old cloth; her stare is at once vacant and intense. Scott Thomas has long had a gift for conveying the roil of emotion beneath a placid exterior and here she uses it to supreme effect. Her thoughts may be opaque but they are not unseen.

Juliette is picked up from the airport by her much younger sister, Léa (Elsa Zylberstein), and their circumstances gradually come into focus: Juliette has been in prison for 15 years, for a crime terrible enough that her parents essentially declared she no longer existed and kept Léa from visiting her. But Léa, as eager to form a connection as Juliette is to avoid one, has welcomed her from prison into the home she shares with her husband Luc (Serge Hazanavicius) and two adopted daughters in the French city of Nancy.

The story itself is less interesting than the care with which it is told. Novelist and first-time writer-director Claudel (who, like his character Léa, is a literature professor in Nancy) parcels details out slowly, and allows the opening of Juliette's tightly folded self to proceed in fits and starts, prodded not only by Léa but also by her kind but melancholy parole officer (Frédéric Pierrot) and a clearly smitten colleague of her sister (Laurent Grévill). This is not a film of grand effects or surprise twists, but rather a series of intimate moments, closely observed and carefully modulated.

That it remains so captivating is a testament to Scott Thomas, whose performance is a tour de force of dramatic understatement. Her Juliette is a beguiling cipher whom we, along with the other characters in the film, cannot but hope to solve, a book that refuses to open. Hints and glimpses of true emotion appear now and then, but Juliette quickly seals them off and seems to examine them clinically, as if they belonged to someone else. After she picks up a stranger in a bar to see what, if anything, sex might mean to her, he confidently asks her "Was it good?" "No, not at all," she answers bluntly. "But it doesn't matter."

I've Loved You So Long runs a bit longer than it perhaps needed to, and the last act contains a revelation, at once unlikely and unsurprising, that robs the story of much of the tension it has accrued. But if his final twist undoes the film to some degree, it cannot undo Scott Thomas's performance, one of the marvels of this, or any, cinematic year.

This post originally appeared at TNR.com.