Caryl Churchill is a 66-year-old publicity-shy barrister’s wife who writes some of the most punk-rock plays in the English language. She has covered a lot of intellectual terrain – feminism, sexual politics, Romania – and has provoked at every turn. Her career teaches that it’s possible, and great fun, to scratch your chin with one hand and give your audience the finger with the other.

Last night, Ms. Churchill made a feverishly anticipated (by me, anyway) return to the New York Theatre Workshop. Two years ago, NYTW presented Ms. Churchill’s “Far Away,” the most striking blend of Hobbes, Orwell, and Vonnegut the stage has yet devised. It imagined a future in which convicts headed for death row must model elaborate hats before a panel of judges, and the entire world goes to war with itself. (“The cats have come in on the side of the French,” somebody reports.) She was showing us our inhumanity, but doing something more: Ms. Churchill’s comic paranoia gave eerily authentic voice to the fear we were all feeling. Crucially, she wrote the play a year before the 9/11 attacks. Ms. Churchill is a prophet of heterodoxy.

“A Number” sees her peering even farther into the future – or does it? The premise tantalizes. What if a 35-year-old man named Bernard, who has grown up as the only son of a widower, discovers his father had him cloned as a toddler? What if he learns he wasn’t cloned – he is the clone? The original son, Bernard #1, is still out there someplace. And Bernard #2 isn’t alone: Unbeknownst to anyone, a doctor created many other Bernard clones, “a number” of them, and released them into the wild. What happens then?

What happens is that Caryl Churchill writes a play about them. Barely an hour long, “A Number” consists of one-on-one encounters between the father, the befuddled, ass-covering Salter, and his “sons.” Cloning may be the pretext for the story, but it’s not really the subject of the play. Ms. Churchill wants to explore personality and how it gets that way. “Nature vs. nurture” only begins to capture these questions. What makes a son a son? she wants to know. Wherein lies the root of Bernard’s Bernardness? And lurking somewhere deep underneath: What might drive a parent to clone a child?

This may sound a little dry, something in the Plato-Stoppard-“CNN Presents” vein. But there’s a penetrating intelligence at work here. Sensitive, bewildered Bernard #2 can’t process the news. “Don’t they say you die if you meet yourself?” he asks his father. A loaded question, as it happens. Because Bernard #1 soon pops up. The sour psychopath wants some answers from Salter, like why he took a bit of his genetic material then “threw the rest of me away.” Salter’s first strategy is to try to get his sons on his side against the doctors who dared to steal their genes: There’s some big money to be made. But mostly he lies. He lies about what he did, what he remembers, how their mother died – anything to push off the blame. The seething Bernard #2 is unimpressed, which turns the play into a kind of Cain-and-Abel story for the Dolly-the-Sheep age.

Real emotional power lurks between the lines of Ms. Churchill’s broken, stuttering dialogue. Maddeningly, that’s where it remains. In London two years ago, the play was directed by the virtuosic Stephen Daldry, who staged “Far Away” so effectively here. James MacDonald, the current director, showed a knack for bold gestures and a faculty with actors in Sarah Kane’s “4:48 Psychosis” earlier this season. As to where those skills have gone in the intervening weeks, your guess is as good as mine.

“A Number” strikes me as a play let down rather dismally by its production. Start with the set. Eugene Lee, clearly feeling gigantic since his

Death-Star-sized scenery for “Wicked” won a Tony, has turned NYTW into an ungainly black box. Gone is the wide, shallow audience. In its place, the company has built a monstrous, semi-circular seating arrangement that rises nearly to the ceiling. The idea seems to be to suggest the operating theater of a medical school: Aside from some dim ceiling lamps here and there and a floor lamp to one side, the action is lit by a massive white instrument beaming clinically down, as if over a surgeon’s table.

I thought the set seemed pretty cool when I saw it: Shake up our frame of reference, and so on. I even thought it was cool when I left. Then I read the play. And I realized that amid all Mr. MacDonald’s exciting innovations, the forced gestures and stilted action, an extraordinary piece of writing had been fumbled. In trying to capture a sense of emotional distance onstage, the production flattens contours that all but leap off the page.

All of Salter’s sons are played by Dallas Roberts, a young actor who has shown remarkable poise and range in plays like “Burn This” and “True Love.” (He also starred in the film “A Home at the End of the World,” but not even he could tempt me into watching Colin Farrell in that wig for two hours.) He shows glimmers of his old, remarkable self here, but all the sons seem under-realized.

The father is played by the top of Sam Shepard’s head. Mr. Shepard hasn’t appeared on a New York stage in a great many years, which may explain why, whenever the scene gets really intense, his face tends to disappear. (The steep seating arrangement doesn’t help.) There’s an ironic thrill to seeing Mr. Shepard, who built his career with stories of beleaguered sons, now playing an beleaguering father. But he seems laconic, almost sheepish, venturing a little way into different reactions, never snapping fully into view. The climax of the play comes when Salter finally tells Bernard #1 the full truth. On paper, it’s devastating; onstage, Mr. Shepard lets it wilt.

Even a lackluster Caryl Churchill production can leave you reeling. At its most potent moment, Bernard #2 tells Salter that he and Bernard #1 both hate him, “except what he feels as hate and what I feel as hate are completely different because what you did to him and what you did to me are different things.” That is bleak, brilliant writing, and it deserves better than it gets here. Somebody ought to put the play in a desk drawer for about 10 years. Dust it off, find two brilliant actors, and give it a production that will hit its every note. People will marvel at how far ahead of the curve Caryl Churchill was all those years ago. It wouldn’t be the first time.

Until January 16 (79 E. 4th Street, between Bowery and Second Avenue, 212-460-5475).