One of the more intriguing experimental features at this year’s Seattle International Film Festival, “Ain’t Them Bodies Saints” is as curious as its title.

Relatively recent Oscar nominees Rooney Mara (“The Girl with the Dragon Tattoo”) and Casey Affleck (“The Assassination of Jesse James by the Coward Robert Ford”) play a passionate, film-noirish couple, Ruth and Bob, who are separated when a shootout lands Bob in a Texas prison in the 1970s.

Ruth did the actual shooting of a police detective, Patrick (Ben Foster), but Bob takes the fall for his pregnant lover.

Patrick survived the battle; four years later he’s obsessed with Ruth and her young daughter.

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Foster brings a wary paternal determination to the character, who emerges as the most vital aspect of the romantic triangle that gradually evolves. But how deep (to coin a phrase) is his love?

The tiny plot revolves around whether Ruth will run with Bob if/when he escapes, or find a more reliable protector in Patrick. Their predicament is almost enough to justify the 90-minute running time.

Almost. Whether you respond to this moody, handsome Western (the luminous “magic-hour” sunset photography is by Bradford Young) will depend almost entirely on how you feel about three characters who can be as hard to read as the vehicle that contains them.

John Hartl: