“The art of losing isn’t hard to master,” Elizabeth Bishop wrote in her poem “One Art,” cycling through objects, people, places, memories, and love. The sentiment’s courage, refined and refuted with insistent ironies, seems suited to the fragile yet tough romance at the heart of “Away From Her,” an achingly moving love story about the impact of Alzheimer’s disease on a retired professor and his flickering wife.

Married for 44 years, Grant and Fiona could illustrate a cover story in Modern Maturity. At their homey cabin overlooking fields and trees, they ski cross-country, flirt over dinner, and read Auden aloud. Grant (played by the Canadian screen icon Gordon Pinsent) is handsome, bearded, of twinkly eye and sonorous voice. Fiona is, to put it simply, played by Julie Christie, one of cinema’s defining beauties and perhaps its most enduring.

When Fiona shelves a frying pan in the freezer after dinner one evening, Grant stops and stares, though it isn’t the first time something like that has happened. Fiona is playful about her occasional lapses, and when they consult a doctor, she is winningly elegant in her recoveries and evasions. But when Fiona gets lost on the way home in sub-zero weather, it points Grant toward her inevitable move under the wing of professional care.

Meadowlake, a respectable rest home with a somewhat impersonal manager, becomes the setting for much of the drama, but the film’s center is embodied by the lifetime of union behind the trauma of physical and mental separation. This is due partly to the heartbreaking performances of Ms. Christie and especially Mr. Pinsent, and partly to director Sarah Polley’s ambitious double-tiered narrative, a skillful adaptation of Alice Munro’s short story “The Bear Came Over the Mountain.”

“Away From Her” folds past and present into each other and moves effortlessly between two consecutive periods: the main story of the run-up and adaptation to Meadowlake, and later, a supporting strand in which Grant enlists the sympathies of fellow Meadowlake “widow” Marian (Olympia Dukakis). Grant’s visits to Marian, we learn, are the result of the unexpected and powerful attachment that Fiona and Marian’s mute husband, Aubrey (Michael Murphy), have formed. Fiona’s devotion to Aubrey is at first a humiliating and confounding blow for Grant, but ultimately it requires him to come to an understanding of and even an appreciation for the bond.

“Away From Her” is therefore not a predictable story of decline and slow-motion farewell but a surprising, risky study of the nature of love. As Fiona describes it, her clingy caretaking of Aubrey is simply less confusing than the bewildering chasms with which her mind separates her from her husband. Aubrey is a welcome simplification, and in the girlish formulas with which she addresses Grant (“My, you are persistent”) on his visits, there’s a touch of regression to more innocent times, which, by the whims of memory loss, are often more immediate.

Our perspective hews closest to Grant, through whom we experience desperately alienated compassion and the agony of fleeting connections. Played with deep sympathy and reserves of toughness by Mr. Pinsent, Grant, like us, never really knows what he will find on his many visits to Meadowlake. He is reduced to sitting and watching his wife watch another man play bridge, but he knows that his being there is enough. Presence and distance, intimacy and absence: Fiona is there and not there, he’s there and a bystander, and so it goes.

Ms. Christie, who has starred in two movies with the 28-year-old Ms. Polley, proves the perfect fit for this part, as often seems to be the case with her roles. Grant’s precise, loving description of Fiona could fit the sexy but ineffably distressed cool that, tinged with a hint of wry playfulness, is Ms. Christie’s hallmark: “Direct and vague, sweet and ironic.” These qualities are all the more tantalizing as Fiona makes do with a kind of life in the present tense, still displaying the “spark of life” that, as Grant likes to repeat, drove him to accept her playful marriage proposal many years ago. That proposal is almost something one could imagine from the Swinging London glamour set that was so closely identified with Ms. Christie early in her career, but it is Grant’s moderately woolly years in the 1970s that come up for evaluation. A sense of guilt nags at him, even though both he and Fiona remark on his loyalty compared with the freer mores of the time. She jokes about all the curious college girls in their sandals, and the camera pans in flashback across young expectant faces.

The film is bolstered by sturdy, expressive filmmaking that underlines the uncertainty of Fiona and Aubrey’s relationship. Grant’s visits to Meadowlake are shot so as to emphasize the distances between the couple, with one particularly moving close-up that seems to strand him. Also successful are the occasional evocations of memory using Super 16 or blurred-bright light (which borrow heavily from the temporally concerned cinematography of Ed Lachman).

Grant’s minor scenes with Marian lack the assured grace of the rest of the film (as do some misjudged scenes of oldster tomfoolery at Meadowlake), though they’re grounded in Ms. Dukakis’s usual canny frankness. But perfection seems a lot to ask of a filmmaker on the underside of 30. Instead of reflexively filming her peers as other young artists might, she has rendered experiences that rarely seem to interest directors who might find them closer at hand. “Away From Her” is a work of deep and unselfconscious empathy. Ms. Polley’s next move will be eagerly awaited.