The hardest thing you can do right now in movies is make one that’s simply original– not based on a novel or a musical or revived from old material. The public is so accustomed now to material that comes from something they know, it’s hard to digest, even market, a complex new idea.

Tom McCarthy, the really terrific Oscar winning writer and nominated director of “Spotlight,” (also the wonderful “The Station Agent,” and “The Visitor”) has done that with “Stillwater.” You could say the idea is not completely original. It’s certainly influenced by the case of Amanda Knox, the American girl who was accused of killing her roommate in Italy. She spent four years in an Italian prison until she was acquitted and released by the Italian Supreme Court of Appeals.

McCarthy, who stuck to the original story for his “Spotlight,” uses Amanda Knox as a jumping off point to write his own version of what might have happened. In the process he’s created the father of the girl in the person of Matt Damon, named Bill Blake. From Cannes much was made of Bill being a Trumper, but it’s not true. He’s asked point blank if he voted for Trump, and responds that he didn’t vote at all.

Bill Baker is no simpleton despite the trucker’s hat planted on his head and his deep, monotonous Southern accent. The voice is almost like Nicole Kidman’s nose in “The Hours.” It’s what you’ll remember about Bill because Damon sounds like he’s deeply scooping up earth with every utterance. His Boston accent from “Good Will Hunting” and his regular voice are so erased, you do forget it’s Matt Damon.

Let’s say “The Martian” was Damon’s best performance in 25 year career of top acting accomplishment. Bill Baker is just beyond that one. Damon is happily submerged into this straight shooter, no frills Oklahoman who’s already been visiting his daughter, Allison, in a Marseilles prison when we meet him. But now she has something to tell him. She knows who the real murderer is, if only he can be found. Bill will have do it since Allison’s lawyer says the lead is a dead end.

Allison is played by Abigail Breslin, the child star of “Little Miss Sumshine” who has grown up to be a fine young adult actress of 26. She and Camille Cottin, the French actress who made such a splash in the TV series “Call My Agent,” make up the two other points of the “Stillwater” triangle. They are just as good as Damon, and hold their own, although Breslin has the advantage because Allison is a character of more shading. Cottin’s Virginie is a little more straightforward, but charming nevertheless.

The story of who killed Allison’s roommate is almost beside the point. McCarthy is really studying Bill as he peels back layers of himself. How far will he go to free Allison from prison? That’s really the question. In the process, how will he change, if at all? This man from Stillwater, Oklahoma (Stillwater is the Rosebud of this story, I think) is out of his element in Marseilles, France. Or is he?

Focus Features should have a box office hit with “Stillwater,” even with a few small logic holes that are better ignored than nitpicked. This is a real tour de force for Matt Damon, easily relatable for men and women. You don’t want to miss it.