B-

Sarah Polley’s debut film, “Away from Her,” was a probing examination of the end of a marriage as a result of a wife’s mental decline due to Alzheimer’s. Her second is also about a couple’s separation, but at an earlier stage in their union, and for quite different reasons. It’s just as acutely observed as her earlier film, if not so painful. But the very deliberate pacing and the obliqueness of the characters’ motivations make it less potent.

In “Take This Waltz,” Michelle Williams plays Margot, a freelance writer married to Lou (Seth Rogen), who’s busy composing a cookbook involving chicken recipes, and so constantly preparing meals in the couple’s Toronto kitchen. On an outing to a period tourist attraction in Nova Scotia for which she’s penning a brochure, she meets handsome Daniel (Luke Kirby), and the two find themselves on the same flight home. Sharing a taxi, they discover that they’re close neighbors.

Daniel, who works as a rickshaw driver, has clearly taken a shine to Margot, and though conflicted she’s clearly attracted to him as well. Most of the rest of the film follows the emotional dance that eventually brings the two together. Margot is clearly in distress, vaguely dissatisfied with her marriage but reluctant to hurt Lou, and the steps toward infidelity she takes are halting and difficult for her. Daniel is more unambiguously eager, though he tries to be cautious in his approaches. And Lou remains in the dark, though in his rather bovine way he’s aware that his wife is growing increasingly distant. There are a few other characters added to the central trio—most notably Sarah Silverman as Geraldine, Lou’s sister, a recovering alcoholic with an almost unbelievably supportive spouse.

Polley skillfully traces the evolution of Margot and Daniel’s relationship in words but even more in gestures that Williams, in particular, handles with great care. After “Blue Valentine,” it’s her second take on a troubled marriage, and while Margot is a very different person from Cindy, the wife in the earlier film, Williams reflects the character’s changing moods dexterously, even if she can’t make the motivations fully clear (after all, they’re probably not clear to the character either). Rogen is much more subdued than usual, but gets across Lou’s teddy-bear quality nicely. Kirby has what is in many respects the most difficult role—he’s the other man, after all, and Polley doesn’t write Daniel in as much detail as she does Margot or Lou. But at least Kirby keeps Daniel from seeming a despicable cad, and he’s allowed even a touch of nobility in the end.

“Take This Waltz” ends with a sense of inevitability as far as the central triangle is concerned. But the last reel adds a plot turn involving Geraldine that seems a rather contrived means to bring the narrative full circle. Still, Polley handles the conclusion with a sensitive touch that keeps it from becoming heavy-handed.

Some viewers will find Polley’s film hard to watch, either because they’ll think it too slow or find it too much a reminder of their own painful experiences. But it’s the rare picture that handles soap-operatic material in a subtle and perceptive way.