I suspect that those who have read Mauriac's novel on which this is based will be disappointed by a film which tells us that Thérèse is troubled by strange thoughts which she hopes marriage will dispel, but gives no indication, until the end, as to what they might be.
To appreciate the story fully, one has to understand the culture of the Landes region around Bordeaux in the early C20, in which prosperous families were preoccupied with their acres of pine forest, contracting marriage with each other to consolidate their wealth and at all costs maintaining their respectability and status.
Thérèse sleepwalks into a stultifying relationship with the forceful and macho Bernard. When his sister, supposedly her best friend, falls in love with an "unsuitable" young man, is Thérèse's failure to support her the result of pressure to be a dutiful wife, or due to less forgivable envy?
Although she is clearly caught in an uneviable position, it is hard to empathise with the chain-smoking, uncommunicative, hard to read, Thérèse. I believe that Mauriac writes a good deal about the "masks" that people assume, but Thérèse is mostly so unemotional on the surface as to seem wooden, inhuman at times. I came to the conclusion that Audrey Tautou, although a beautiful and talented actress, is miscast here. The part needs to be played by a younger actress who comes across more convincingly as inexperienced and malleable, yet unpredictable.
As the plot darkens, some of the details are annoyingly unclear, but the story is unusual in taking an unexpected direction as it moves to a rather inconclusive ending. Beautifully shot and well-acted, it left me feeling unsatisfied, and I don't know whether to blame Mauriac or the director.