When May becomes pregnant, she prays for a boy, observing that Xuan, who has given birth to two daughters, holds a lower status than Lao, the mother of sons. She also observes the affair between Xuan and their husband’s oldest son, a relationship that brings conflict and tragedy to the clan and some heavy-breathing al fresco eroticism to the film.

The sensuality that Mayfair and Chananun Chotrungroj, the director of photography, create around May is seductive, and also unnerving. “The Third Wife” presents a tableau of injustice — a male-dominated hierarchy that directly oppresses women and brings collateral misery to some men as well — from a perspective that feels both compassionate and detached. It’s too cool for melodrama and too pretty for politics, and the drama of May’s experience occupies a middle ground between pity and indignation.

The cruelty she encounters is a fact of life, as is the solidarity she occasionally experiences with Lao and especially with the unfailingly kind Xuan. The possibility of freedom occasionally stirs like a faint breeze, and the film’s final scenes hint at desperate and defiant acts of resistance. But the movie is also trapped in the same claustrophobia it depicts, unsure of how much it can or wants to get away with.