Review: 'The Card Counter' is a sly and absorbing character study of a gambler on the brink.

Like the diamond-sharp movies he used to write for Martin Scorsese — a Murderer’s Row of films that includes “Taxi Driver,” “Raging Bull” and “The Last Temptation of Christ” — Paul Schrader creates in his new film, “The Card Counter,” a fascinating study of a loner whose past and present collide.

Oscar Isaac stars as the title character, who has taken the alias William Tell as he travels from casino to casino across the country. He can keep track of what kinds of cards have been played at the blackjack table, which allows him to win consistently. He usually leaves the table before he wins too much, before casino security can get wise and throw him out. Bill, as he sometimes is known, does catch the attention of La Linda (Tiffany Haddish), a pro gamer who keeps a stable of card players, finding them investors who will stake them in big tournaments.

Schrader, who wrote and directed, reveals early on that Bill learned card counting in prison. Soon, Schrader also reveals the prison was in Leavenworth, Kan., and Bill’s crime was his involvement in the torture and humiliation of prisoners at the Abu Ghraib prison in Iraq. The ones in the pictures, Bill remarks in the running narration, got prison time; their superiors, and their superiors’ superiors, did not.

In the convention center of one casino, Bill walks into a law enforcement conference and sits in on a lecture by a Maj. John Gordo (Willem Dafoe). A flashback shows us that Gordo was a civilian contractor in Iraq, who ordered around Bill and other men to commit the atrocities that led to Bill’s incarceration.

Back in the present, Bill also notices a young man looking very intently at Gordo. The man introduces himself as Cirk — “‘Kirk’ with a ‘C’,” he tells Bill. Cirk explains to Bill that Gordo also commanded Cirk’s father during the Iraq War, and that Cirk blames Gordo for his dad’s PTSD and suicide. Cirk tells Bill he has a plan to kidnap, torture and kill Gordo.

Bill then does something uncharacteristic for him: He gets involved. Bill takes Cirk under his wing, bringing him along on the road, as he takes up La Linda’s offer to get into the lucrative World Series of Poker, which could end with a run in Vegas.

As he did in his last film, “First Reformed,” Schrader creates a self-contained little world in which the main character — Isaac’s guilt-stricken gambler here, Ethan Hawke’s haunted priest there — wrestles with ghosts from his past while being prodded to take action in the present. If Bill is a bit enigmatic, that’s to be expected, given the nature of card playing, and of the size of the demons he’s facing.

Isaac leads a solid ensemble cast with under-the-radar intensity, conveying through small gestures and Schrader’s economical dialogue Bill’s desire to live quietly and make small jackpots where he can — while also seeing this kid as a chance to atone for past mistakes. Isaac’s performance is one of the best you’ll see all year, one that will be admired for its honesty and quiet menace.

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‘The Card Counter’

★★★1/2

Opens Friday, September 10, in select theaters. Rated R for some disturbing violence, graphic nudity, language and brief sexuality. Running time: 109 minutes.