The first time I saw Kelly Macdonald in 1996's “Trainspotting,” probably the last film I would have expected to see her in 22 years later was an understated slice-of-life film like “Puzzle.”

Macdonald plays Agnes, a middle-aged mom so accustomed to caring for others that the film opens with her decorating her family's house for what turns out to be her own birthday party.

Agnes is stuck in the sort of midlife suburban rut that could have inspired Shel Silverstein's “The Ballad of Lucy Jordan,” with a genuinely loving yet deeply thoughtless husband, Louie — played by David Denman, in what amounts to a retread of his well-meaning but stunted character from “The Office” — and a maddeningly predictable day-to-day life.

We see Agnes' meticulous nature when she hunts down the final fragment of a plate that was accidentally broken by Louie, and this latent talent for figuring out how pieces fit together comes in handy when she decides, one idle day, to break out the jigsaw puzzle set she received as a birthday present.

A quest for more jigsaw puzzles leads the sheltered Agnes to take the train into New York City, where she spies a flier asking for a “puzzle partner” in an upcoming jigsaw puzzle assembling competition, which leads her to independently wealthy former inventor Robert, played by Irrfan Khan as an indolent intellectual, with an affectedly dissolute air about him.

There's an entire sub-genre of films devoted to following the evolution of newly empowered women, so it will likely come as little surprise how the influence of the worldly and sardonic Robert encourages Agnes to start following world news, and asserting herself against the gently condescending whims of her family.

But what's interesting is Agnes ultimately calls Robert out for wallowing in the tragedy of real-life catastrophes, and not applying his considerable brainpower to more constructive ends.

Likewise, while Louie's outlook on life is limited, and his treatment of both Agnes and his older son — Ziggy (Bubba Weiler), who wants to become a cook like his mom — borders on outright bullying, the film does not reduce him to a stock made-for-Lifetime-TV villain.

This film has such potential in portraying the mental and therapeutic benefits of such a seemingly simple and meaningless exercise as assembling a puzzle that I can't help but lament its inclusion of a romantic subplot between Agnes and Robert, as was already spoiled by its trailers.

Macdonald and Khan are capable enough actors, and the puzzle-assembling styles of Agnes and Robert already feature enough frisson of contrast in their respective approaches to life, that it just seems reductive to have Agnes give in, however momentarily, to Robert's come-ons.

While the film avoids allowing Agnes either to settle for the malaise she knows with Louie, or to jump heedlessly into a whirlwind romance with Robert and all of his unpacked issues, the narrative's attempt to offer her a third way could have used a bit more development beforehand, since it leaves more questions than it answers.

Watch this one for Macdonald and Khan, but be prepared for some disappointment at its lack of a clear resolution.