Early in “McReele,” Stephen Belber’s new play at the Roundabout, Darius McReele stands, hands clasped before him, imparting some sophisticated ideas about public policy. Are his fingers laced this way because he’s thinking deeply about the minutiae of welfare reform? Or is it because he’s wearing handcuffs that limit what the convict can do?

Darius McReele is a smart, conscientious, charismatic black man. He is also sentenced to die, for a murder he allegedly committed when he was 17.The play begins when an article he wrote for the prison Web site is discovered by a middle-aged white journalist, Rick Dayne. Rick reopens Darius’s case, and gets his conviction overturned. Darius speaks out on a couple of fashionable causes, and before long the state Democratic Party wants him to run for the Senate. “You’re everything we’ve ever wanted,” says the charmed politico. He’s got a good shot to win.

You could play this story any number of ways: as political satire, say, or as social indictment. Mr. Belber takes a somewhat broader view. The play is never explicit about what happened the night of the crime, and never tells us exactly what happens to Darius in the end. Instead it uses a series of compelling “What if” scenarios to challenge our ideas about the ethics of media and politics. (What if someone with Barack Obama’s gifts – the comparison is inescapable – had come from jail instead of Harvard Law?) Mr. Belber invites us to think about the differences between what people say and what they do.

Or rather, between what they do and what they’ve done. In Mr. Belber’s plays, every closet has its skeleton. Jon, the high-minded filmmaker in “Tape,” committed a terrible sexual assault as a teenager, and thought he had gotten away with it. Tobi, the ingratiating dance instructor in “Match,” horribly mistreated a lover decades earlier. He thought he had gotten away with it too.

“McReele” falls somewhere between those two efforts. It suffers from some of the thinness that plagued “Match,” but uses richer raw material. It works on a broader, more ambitious canvas than “Tape” (in a tentative way, “McReele” is one of the most political plays New York has seen in years), but lacks the earlier work’s provocation and emotional punch.

Here Mr. Belber finds himself in a stylistic trap. He works in a vein of strict domestic realism. This means no juicy soliloquies from Darius to tell us when he’s really contrite and when he’s just manipulating somebody. Yet some of the plot particulars are so contrived that it’s hard to buy the reality of any of it. Rick quits his job to run Darius’s campaign. He also dates a local television-news personality, a woman named Katya who just happens to be the host a town-hall-style forum for Darius and his opponent. I could maybe see the charmingly feckless Democrats standing for that, but it’s hard to imagine Darius’s Republican opponent going anywhere near the stage.

Director Doug Hughes lends pace and focus to Mr. Belber’s play, despite some wobbly casting. Rick, the guilt addled journalist, is supposed to be weaker than Darius, putty in his super skilled hands. But Michael O’Keefe brings almost no weight to the role, no interiority. As Katya, a series of plot necessities lashed together and given a name, Jodi Long doesn’t fare much better.

Fortunately the other actors are extraordinary. In a series of small roles – the Democratic operative, the Republican opponent, the victim’s aching father – Henry Strozier finds remarkable depth and grace. Portia, who has distinguished herself with the Labyrinth Theater Company recently, plays Darius’s wife affectingly: a bundle of raw nerves beneath an iron veneer. She tips into excess now and then, but the show would be lost without her poise and comedy.

As Darius, Anthony Mackie continues to prove he’s one of the most gifted and promising young actors around. He sparkled in his Broadway debut, “Ma Rainey’s Black Bottom” and almost performed the impossible by redeeming “Drowning Crow”. (In a recent interview, Mr. Hughes said he offered Mr. Mackie this role without an audition – a credit to both of them.) Here, wearing a kind of junior-Lenin goatee, he manages to convey Darius’s intelligence, charisma, and effortless manipulative power; he is sometimes mesmerizing. But this is not to say that everything works. Some of the most banal moments – quiet conversations with Rick, sudden reactions – feel forced. The relative inexperience shows.

Still two reasons for hope bear mentioning. When he’s acting opposite strong actors – like Portia and Mr. Strozier – Mr. Mackie gets sharper. Even better, his performance takes on new power and flair in scenes with a heavy emotional charge. That is, the more that’s asked of him, the more he delivers. So I’ll ask again: Would some wise producer please secure this young gentleman a shot at the classics, and bar Hollywood casting agents at the door?

***

Irish Rep has revived Samuel Beckett’s “Endgame,” and that is cause for joy. Charlotte Moore’s production isn’t a Beckett for the ages, but it does a mostly commendable job of keeping this dark, comic, apocalyptic masterpiece before a New York audience. As master and servant Hamm and Clov, Tony Roberts and Adam Heller take an offhand approach to the otherworldly dialogue. It doesn’t have quite the resonance it should; it feels a little domesticated. The two of them made me think (unhelpfully, to be sure) of Larry David. But Mr. Roberts has that rich, million-dollar voice, and after all his years in the business, knows how to use every note of it.

The show’s real triumph, and true attraction, is Alvin Epstein’s Nagg. In the 1950s, Mr. Epstein appeared in the American premieres of “Waiting for Godot” and “Endgame.” The revival promises a chance to see Beckett as it ought to be performed, and Mr. Epstein doesn’t disappoint. This is style completely in the service of text: A believable character in an unbelievable situation. One effect of Mr. Epstein’s finely etched performance is to show the shortcomings of the work that surrounds him; another is to redeem it. Ms. Moore isn’t the only one who’s lucky to have him.

“McReele” until May 1 (111 W. 46th Street, 212-719-1300).
“Endgame” until April 10 (132 W. 22nd Street, between Sixth and Seventh Avenues, 212-727-2737).

WHAT TO SEE THIS WEEK

‘Shockheaded Peter’ Ohio Theater
Giddy ghoulishness (and vice-versa). (212-868-4444)

‘The 25th Annual Putnam County Spelling Bee’ Second Stage
Charming nerds on parade. (212-246-4422)

‘Boozy’ Ohio Theater
Clever, tricksy presentation of ‘The Passion of Robert Moses.’ (212-239-6200)