The creators of “Sin (A Cardinal Deposed)” have done a singular public service. Like so many docudramas lately (“Guantanamo,” “The Exonerated”), the play is based on the public record. Michael Murphy assembled the script primarily from transcripts of depositions given by Cardinal Bernard Law two years ago, during the civil suits arising from the clerical sex abuse scandals.

And, like so many of its predecessors, this docudrama has a muckraking intent. Mr. Murphy wants to appall you with a true account of how priests in the Boston archdiocese and elsewhere were allowed to continue preying on children. This he certainly does. Cardinal Law has no response when a woman, playing the mother of an abused boy, reads from a letter she had written. When she confronted her son with news that he had been molested, the boy “was crying and shaking. He told me that Father John Geoghan said that I wouldn’t believe him. That I … had too much faith in the church … and that I wouldn’t believe him.”

No Hollywood villain could be more evil. Geoghan and the other priests who abused their young charges repeatedly compounded the sin of lust with the more serious sin of pride. And if it wasn’t clear before, this play makes it obvious that Cardinal Law and other officials in the Church hierarchy committed that sin as well. His willful ignorance, his weak denials, and his unconvincing apologies are awful to behold.

For anyone who followed the scandals as they unfolded, “Sin” will renew an old sense of horror. But at the Clurman Theatre, where The New Group opened the show last night, you may also have a second, unexpected reaction. Scenic designer Nathan Heverin has assembled a set of total banality. We see a conference room. It has ugly green walls and ugly beige chairs, and a potted plant, and a water cooler. This hardly seems like the spot for a radical event in human history, but that is not the greatest of the scandal’s surprises.

Because, what, really do we witness? At this end of the table sits one of the most powerful figures in the most powerful religious organization in the country. At the other sits a lawyer, not even a particularly impressive specimen of the breed. Mr. Murphy has created a composite of the attorneys who questioned Cardinal Law. As played by Thomas Jay Ryan, Orson Krieger is affable, deferential, dogged. No Dershowitz theatrics; no Darrow masterstrokes.

Yet if you step back, and take a long view, their interaction may take your breath away. An ugly paradox lies in the fact that religion, which is supposed to liberate, often enslaves. Put religion in close proximity to state power and the situation grows even more dire. But this bland little conference room could not be further from the Inquisition, or Shariah law, or even the horrors of Salem. In the matter of Geoghan, Shanley, and the abused children, priests failed the people. But in this country, for once, the law is on the people’s side. “Sin” shows us the third estate demanding justice from the second, under the protections of the first.

Viewed historically, this is thrilling, even when the action of the play sometimes is not. Director Carl Forsman resists what must have been a very great temptation to make the show too sexy. Nobody flips the table over. Yet you forgive the occasional tedium, because lawyerly squabbling is preferable to most of the alternatives tried over the years, and because of the wonderful bursts of impertinence. “Cardinal Law,” the victims’ lawyer asks, “are you familiar with what a mortal sin is?” He exercises the right to intrude in the very heart of the cardinal’s affairs. The cardinal’s only recourse is to get his own lawyer to defend him.

The show premiered in Chicago early this year. Its new cast features Mr. Ryan, who is just right as the victims’ attorney, though John Leonard Thompson tends to one-dimensional stridency in his defense of the cardinal. Dan Daily and Cynthia Darlow play all the secondary roles from the sides of the stage: Angry mothers, worried doctors, priests who damn the cardinal with his own words. Pablo T. Schreiber’s monologue at the end of the show left the audience sitting in horrified silence. I wonder if people realize that his speech is even more devastating than it sounds: Patrick McSorley, the victim he portrays, has since died of a drug overdose.

John Cullum plays Cardinal Law with an air of perfect superiority. Intentionally or not, he sometimes finishes an answer with a grim, Rumsfeldian smile. If you only listen to Mr. Cullum’s words, and don’t look at his priest’s black attire, or bishop’s ring, he could be any powerful figure in American life today. Any figure, that is, who has been led away from the path of service, and corrupted by the presumptions of power. Take your pick: bishops, corporate directors, politicians. More and more they share the mistaken belief that we work for them, and not the other way around.