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Regina King makes an assured feature directing debut with “One Night in Miami,” an engrossing adaptation of Kemp Powers’s 2013 stage play.

In that well-received drama, Powers wrote about what might have happened on Feb. 25, 1964, when a cocky young boxer named Cassius Clay beat Sonny Liston for the world heavyweight championship; later that night Clay, Nation of Islam leader Malcolm X, pop singer Sam Cooke and NFL star Jim Brown gathered in a hotel room to celebrate. No one knows for sure what they talked about, but Powers concocted a riveting piece of historically grounded speculation, in which the four men debate Clay’s decision to become a Muslim, the political advantages of assimilation versus revolution, the responsibilities of Black men to their communities, and why vanilla ice cream is no match for a flask full of whiskey.

The vanilla ice cream, by the way, is one of the few facts known about the evening that inspired “One Night in Miami” — it was offered as a refreshment by the gathering’s host, Malcolm X, whose religion forbade anything stronger. As the night plays out, tensions rise as the four men — all, it should be remembered, in their 20s and 30s — joke and argue, tease and provoke. Although Brown and Cooke are skeptical of Malcolm’s sway over Clay, emotions truly come to a boil when Malcolm confronts Cooke over his music, making an unflattering comparison to Bob Dylan, the White man who had written the era’s most stirring anthem of dissent.

Powers’s script can’t help but suffer from expository starchiness, having to educate present-day viewers about what may feel like ancient history. That makes it all the more crucial to find actors who can deliver the lines with unforced ease, and King has found just the right ensemble. The British actor Kingsley Ben-Adir plays Malcolm X with a convincing combination of reflection, fury and growing anxiety (he is harboring his own doubts about the Nation of Islam and is all too aware of the men who have him under surveillance outside the hotel); Leslie Odom Jr. effortlessly sinks into Cooke’s charismatic persona, while he soars into the singer’s distinctively honeyed tenor; Aldis Hodge inhabits Brown with imposing, watchful confidence; and Eli Goree brings just the right amount of humor and poetic cadence to his exuberant portrayal of Clay, who at one point does a double take in front of a mirror, saying, “My goodness. Why am I so pretty?”

As a filmed version of a play, “One Night in Miami” has the same talky, slightly claustrophobic contours one might expect. But that pent-up quality is an advantage for a movie in which the room where it might have happened is a character in itself. The Hampton House Motel was a famous way station for African Americans traveling during the days of segregation; here, production designer Barry Robison gives it an attractive mid-century sheen, amped up by Terence Blanchard’s silky musical score and Tami Reiker’s lush cinematography. In both its verbal sparring and mounting unease, “One Night in Miami” resembles the recent Netflix adaptation of “The Boys in the Band” — another period piece that gives viewers the sense that they're eavesdropping on a conversation taking place both amid and beyond the reach of societal oppression.

To her credit, King takes a few judicious opportunities to open up the action in “One Night in Miami,” which includes scenes on the motel’s rooftop and a nearby package store, as well as an electrifying flashback to one of Cooke’s concerts. Most powerfully, she gives each protagonist a prologue, telegraphing where each man is in his personal and political evolution. Jim Brown’s chapter is the most potent in the collection, following him as he visits his hometown of St. Simons Island, Ga., and pays a call to an elderly friend played by Beau Bridges. King takes her time with the scene, allowing it to play out with the relaxed rhythms of a sunny afternoon on the front porch, before delivering a finale that lands like a punch to the gut. It's a masterful piece of cinema — a self-contained film within a film — and it signals that King's directorial career is off to an exceptionally promising start.

R. At area theaters on Jan. 8; available Jan. 15 on Amazon Prime Video. Contains strong language throughout. 110 minutes.