MATT DAMON stars in “Stillwater.” (Focus Features).

By Jim Tortolano

Matt Damon burst onto the big league cinema scene in 1997 as the smart but rough-edged math genius in “Good Will Hunting.” Although in reality he had an upper middle class upbringing – prep school and Harvard – Damon is at his best being the good guy working class hero, as he is in “Stillwater.”

Damon is Bill Baker, a roustabout dad from Oklahoma whose free spirit daughter goes to France and is convicted – perhaps unjustly – of a murder and sent to prison.

Square-jawed and laconic, Baker is determined to figure out a way to get Allison (Abigail Breslin) out of stir by any means necessary. Nearly stymied in his task, he is befriended by Virginie (Camille Cottin) and her daughter Maya (Lilou Siauvaud), who help him navigate a different culture, language and more.

As you may know, “Stillwater” is based on the real-life story of Amanda Knox, so considerable liberties are taken. Strong performances by the principal actors carry the story along, although the film drags in places as if writer-director Tom McCarthy wanted you to feel how repetitive and frustrating Baker’s mission is by drawing the story out about 20 minutes longer than it needed to be.

Another notable aspect of the film is that it shows poverty, racism and institutional ennui exist in every country and society, making connections between the dirty fingernail town of Stillwater and the rougher parts of Marseille in France.

Bill and Allison each evolve into more accepting people, and there’s a twist toward the end that makes the 140-minute running time almost worth the fat in the screenplay.

But watching Damon do his understated thing is definitely another signpost in a distinguished acting career. In this movie, still waters run deep.

“Stillwater” is rated R for language and violence.