AN OLD MAN sits alone in an armchair, his back to us. He wears a gray suit over a rumpled shirt; he's smoothing back his hair. Periodically the man swivels his head around, ignoring us, looking for someone in particular who may never arrive. He sweats, he smokes and he remains alone with his troubling thoughts.

This quietly surprising scene is what greets audience members as they file into Studio Theatre's production of Caryl Churchill's "A Number." The play takes on the hot-button issue of human cloning, but its real target is the age-old conflicts between parents and adult children. Churchill's writing has been likened to Shakespeare, what with its parsimony, word play and use of rich colloquial language. Like the Bard's plays, there are few stage directions, leaving the Churchill play open to a host of interpretations.

"It's an unrelentingly pure script," says Joy Zinoman, the director of "A Number" and Studio's artistic director. Upon seeing the original production in London, she "was very moved by it and wanted to do it here," having directed an acclaimed production of Churchill's "Far Away" at Studio last year. Zinoman saw a second production at the New York Theatre Workshop, which dissatisfied her. "It was cool, it was minimalist in the acting," she says, with a lavish "Crate and Barrel"-style set and frequent costume changes. "I thought it lacked the mystery, [and] I felt very strongly that the New York production should not be the direction that the play takes in America." In line with Churchill's "pure" script, the Studio set offers the bare minimum -- two chairs and a shag rug -- so the emotions of the father and his sons can take center stage.

One of Zinoman's key directorial decisions was the lonely opening image of the father of the family, Mr. Salter (Ted van Griethuysen). "I think Caryl Churchill says, if I remember correctly, that the play takes place 'where Salter is,' " says van Griethuysen. "It doesn't define it any more than that." Restless, shifting in his chair, the actor wordlessly conveys his anxiety about the imminent confrontations he must have with his sons resulting from the secrets he has kept from both.

The sons, Bernard One and Bernard Two, are played by Tom Story, who has the unique challenge in "A Number" of bringing to life two genetic clones who are very different individuals. "They are definitely . . . separate characters, but they are played through the core of me, so it works," Story says. He uses a few gestures to indicate the clones' biological link, for instance turning and shrugging one shoulder "like they all have stiff necks . . . it's a physical habit." Gestures are also used to differentiate the sons. Bernard One, a roughneck, is "always trying to be cool . . . so that people will think he's tough." Story behaves accordingly, stalking around the stage with his shirt sleeves rolled up to show off impressive biceps. The exchanges with his father are equally defiant; he steadfastly refuses to make eye contact when Mr. Salter speaks.

The other son, meanwhile, is a sensitive and self-protective soul. "He's uncomfortable in his own body," Story says, "always trying in some way to get away from the father because he's so pecked by him. . . . My impulse was to hold myself in, or curl in on myself."

The push and pull of the sons' interactions with their father recalls every family's arguments and the conflicted desires of its members. And although the Studio Theatre's production of "A Number" lasts only an hour, it's emotional intensity makes it feel like a full-length play.

"It's exhausting," van Griethuysen says. Exhausting but necessary, according to Zinoman. "I know them to be actors of great intelligence and . . . of great emotional power, which I wanted to tap." There's no other way to tell a story so "epic . . . [reflecting] the most complex times of families in the middle of the night."

Clone war: A father (Ted van Griethuysen) confronts one of his two cloned sons, both played by Tom Story.