The Scottish actress Kelly Macdonald is a versatile talent who has handled a variety of roles over the last 20-plus years, but she’s best known for roles as the girlfriend or the wife.

Macdonald made her film debut in “Trainspotting” as the schoolgirl who meets and hooks up with Ewan McGregor’s Renton in a club. She played Margaret Thompson, wife of Steve Buscemi’s Nucky, for five seasons on HBO’s “Boardwalk Empire. She was spectacularly good as Josh Brolin’s wife in “No Country for Old Men.”

In the understated and quietly moving “Puzzle,” Macdonald is once again playing a wife and mother — and a subservient one at that, at least when we first meet her — but it’s the lead role in the story, and how wonderful it is to see this fine actress carry a film and carry it so beautifully.

Macdonald plays Agnes, a stay-at-home mother in Bridgeport, Connecticut, who never stops tending to the needs of her old-school husband, Louie (David Denman), who owns a garage, and their teenage sons Gabe (Austin Abrams) and Ziggy (Bubba Weiler), who are both struggling to map out their futures.

Even at her own birthday party, Agnes is almost an afterthought. She busies herself serving the guests and has to bring out her cake from the kitchen.

It appears as if Agnes has received all of two gifts for her birthday: an iPhone, which doesn’t do anything for her, and a 1,000-piece jigsaw puzzle.

THAT gets her attention, for reasons Agnes probably can’t even explain. She pours out the pieces and gets to puzzling, and discovers she’s something of a savant, with a natural ability to see the big picture, so to speak, and piece it together with astonishing clarity and speed.

Agnes learns of a puzzle store in Manhattan and takes the train to the city for the first time in years.

At the specialty store, Agnes sees an ad from someone looking for a puzzler partner for an upcoming tournament. Wouldn’t you know it, that someone turns out to be the handsome, wealthy, brilliant and recently separated Robert (Irrfan Khan). Robert is dazzled by Agnes’ puzzling skills and drawn to her warmth and strength; Agnes feels alive in the presence of someone who is actually interested in what she has to say.

Director Marc Turtletaub deftly builds the dramatic tension as Agnes tries to maintain a double life of sorts (for a long time, her husband and children know nothing about her interest in puzzling, let alone her puzzling partner).

Putting together a puzzle is easy for Agnes. Fitting together all the pieces of a life that has unexpectedly grown more complicated — and more fulfilling — is going to be a challenge, no matter which path she chooses.

This is Agnes’ story and this is Kelly Macdonald’s movie.

“Puzzle”

102 minutes

Rating: R for language