I hadn’t planned on writing about “The Homesman,” but it wouldn’t let me go. When I first saw the Western — directed, co-written by, and co-starring Tommy Lee Jones — last week at Sundance Cinemas, I walked out of the theater not sure how I felt about it. The jumble of tones, the ambiguity of the performances, the jarring plot turns, and above all the stubborn refusal to play by the rules of the Western — I just wasn’t sure what to make of it. I’m glad I didn’t have to turn around a review for the next morning.

But “The Homesman” has stuck with me, and over the last few days my thoughts have formed into an appreciation for this strange and sad movie. Today (Tuesday) is its last day at Sundance, as it makes way for the new “Hobbit” movie, so this article likely won’t do you much good. But I still highly recommend you seek it out somehow.

Jones has always carried himself with an air of contrarian cantankerousness, and in his films he literally goes the opposite direction from anybody else. In his debut as a filmmaker, the sublime “The Three Burials of Melquiades Estrada,” Jones painted a sympathetic portrait of the immigrants flooding into his native Texas from Mexico by going the opposite way, telling the story of two Americans who escort a dead Mexican friend from Texas back across the border to bury him in Mexico.

Similarly, “The Homesman” is a Western that heads east. Mary Bee Cutty (Hilary Swank) is a tough, good-hearted pioneer woman in Nebraska who has agreed to take three women back east to Iowa. No two ways about it — the frontier has broken these women, driven them insane by hunger, abusive husbands, children dying of disease. It’s an unsettling glimpse into the underside of the pioneering American spirit — for every one who makes their fortune in the untamed frontier and gets a street named after them, there are many more who fall by the wayside, broken and used up.

Although Mary seems to have adjusted to the rigors of the frontier life, there are signs that she is not too far behind these women. Unmarried, she hides a deep well of loneliness beneath her flinty exterior. In an extraordinarily controlled performance, Swank just breaks your heart. In an early scene, she makes dinner for a neighboring farmer, then proposes the idea of marriage — extolling not her own feelings or desires, but the financial benefits of the arrangement. The farmer, no prize, turns her down flat, calling her “bossy” and “plain.” That is Mary’s prize for being a woman able to survive in such a harsh world — to be denigrated and cast aside for doing so.

So Mary is not leaving much behind when she agrees to take the women east. Along the way, she hires a drifter, George Briggs (Jones), to help her. A cheerfully unsentimental sort, George sees nothing noble in their pilgrimage east to help the women — “There’s $300, and that’s it,” he tells Mary. The harsh landscape, often just a thin line on the horizon separating one shade of gray from the other, seems to echo George’s pitiless worldview rather than Mary’s Christian spirit.

We assume that, over the long and arduous journey, Mary and George will face hardships and dangers, and a bond will grow between them. They do indeed face dangers including Tim Blake Nelson as a grinning killer (the movie is packed with great character actors in small, juicy roles). And a wary respect is fostered between George and Mary, even if they’ll never quite see eye-to-eye.

And then their relationship completely shifts in an instant, in a way that is both shocking and, in retrospect, understandable and probably inevitable. I won’t reveal what happens, but it is the sort of shift that makes you completely re-evaluate the characters and their relationship to each other, and yours to them.

It’s a daring move in any sort of movie, but in a Western, a genre that often adheres to some strict archetypal rules, it’s extremely jarring. But Jones isn’t interested in making a movie about archetypes; he’s making a movie about people.

And people can surprise you. “The Homesman” certainly surprised me, and still haunts me.