Perhaps the greatest distinction of David Mamet’s fine new film, “Redbelt,” is that it lasts not a second longer than necessary: The curtain falls precisely when all that really matters has been said and done. In many ways his most straightforward film, “Redbelt” is a ruthlessly executed tale of cloistered warrior honor exposed to the open air of a fallen world. In other words, it’s an old samurai story, but Mr. Mamet’s clockwork mechanism is downright cathartic and his leading man, Chiwetel Ejiofor, is charismatic enough to watch indefinitely.

A jujitsu struggle introduces us to Mike Terry (Mr. Ejiofor), an expert in the Brazilian fighting style who is coaching self-defense at his spare, mixed-martial-arts academy in Los Angeles. Like many Mamet heroes, Mike sometimes seems capable of speaking exclusively in koans (“Everything has a force. Embrace or deflect it; why oppose it?”). But this man with a code is going broke, and must lean on the resources of his Brazilian wife (Alice Braga), a struggling designer.

What distinguishes Mike’s training regime is its random element — each student basically draws a lot to determine who will fight with a handicap — and, accordingly, it is a random event that sets the interlocking logic of the plot in motion. Part of the satisfaction of Mr. Mamet’s yarns is the lucid-dream surprise of watching how contingent details click into place.

First, an unstable lawyer who’s been through a trauma (Emily Mortimer) walks into Mike’s studio just as the night class is adjourning. When she suddenly becomes frightened by Joe (Max Martini), a cop and student of Mike’s, a gun registered under Joe’s name goes off. Later, when Mike goes to check on Joe at his off-duty job as a bouncer, he winds up saving the skin of a movie star named Chet Frank (Tim Allen) in a smoothly choreographed bar fight.

From the not so equal and opposite reactions to these initial outbursts, “Redbelt” plots out the collision of two systems of thought and action — honor and cash. Chet, his dissolute air notwithstanding, rewards his rescuer with a dinner invitation and work as a consultant on his Gulf War film. But suffice it to say, Mike and his wife find their good fortune hard to navigate. Strapped for cash, the principled teacher enters a tawdry mixed-martial-arts championship that is telecast live and masterminded by the sardonic Marty Brown (Ricky Jay).

By this point in the description — or in Mr. Mamet’s career — most readers can judge for themselves whether this sounds ridiculous or like prime fodder for the playwright-filmmaker’s theorems on persuasion and artifice, discipline and gamesmanship, wit and wisdom. Even after two decades of directing mannered, intelligent-design worlds, Mr. Mamet’s work still feels at once alien and intimate, spoken in its own mishmashed argot of ventriloquized cynicism and riddling B-movie phrasemaking speckled with anachronisms.

What grounds this endeavor is the often mournful serenity of Mr. Ejiofor, who, like the fighter he portrays, intuits when is the right time to hold back. Most genre pictures extolling dignity and honor bank on the lead simply and nobly embodying those qualities, but this actor makes you believe the less credible bits of a Mamet character. (He also looks periodically beatified under cinematographer Robert Elswit’s expert eye.) Mike’s authority comes from restraint, which Mr. Ejiofor portrays as both a strength and a weakness as Mike wades through Mr. Mamet’s usual school of sharks.

“Redbelt” doesn’t hinge on the false-bottom cons and double crosses, as in many of Mr. Mamet’s past films. Mike and his imbroglio with unscrupulous characters recall Campbell Scott’s naive, flawed scientist in “The Spanish Prisoner” (1997) and his sudden woes. But this milieu is dotted with gestures of authenticity, including locker-room posters at Joe’s precinct selling used revolvers, the constant chatter and announcements in the championship prefight room, the casting of cauliflower-eared Ultimate Fighting alumnus Randy Couture as a game announcer, and the casting of Ms. Braga and fellow Brazilian actor Rodrigo Santoro (as her brother).

Some of Mr. Mamet’s films have been read as satirical allegories for filmmaking, but since he titled his compilation of Hollywood-related writings “Bambi vs. Godzilla,” the idea seems a bit redundant. Rather, the experiences of the magnanimous hero in “Redbelt” could suggest that big spectacle can be an opportunity to demonstrate honor rather than an automatic debasement. An uplifting David Mamet movie? It’s just one more surprise from a frequently mocked writer who’s still beating Hollywood at some of its own games.