What a gift John Patrick Shanley gave to middle-aged-and-over actresses when he brought Doubt to the stage. The role of Sister Aloysius is the sort performers dream about: dominating, unpredictable, withering, unwittingly comic, getting by not on glamour but on ugly old self-righteousness, mean-spirited certainty and unflappable overconfidence. Sister Aloysius is a Dirty Harry of a nun, unbothered by fine moral distinctions, and willing to plug any culprit she suspects of malfeasance, sufficient evidence or not. She's the perfect anti-heroine for our youth-obsessed, politically correct culture, the Shadow figure we've all repressed in favor of Miley Cyrus. Sure, she's a bad-tempered old prune. Nevertheless, she's quite wonderful. All she's missing is a pistol and the words "Make my day."

Still, she does have tricks of her own — and as played by Christine Decker in the fine production at American Stage (which I saw in a preview), she's willing to use them all to demolish a young priest whom she suspects of sexual misconduct. In case you've already seen the film with Meryl Streep as Aloysius, let me assure you that there's still reason to visit the stage version starring Decker. As Streep played the part, there was something human in this surly Sister; not so at American Stage. As intelligently directed by Todd Olson, Decker is cold, crabbed and crusty, a woman with no one to please but herself and her steel-trap conscience. And this seems right: who made the rule that theatrical characters need redeeming qualities?

If we're looking for more pathetic figures, we can find them in Father Flynn, the popular priest who may or may not be an abuser, in Sister James, the naïve young nun who wants to believe the very best about people, or in Mrs. Muller, the beleaguered woman whose son's innocence may have been violated. These are the ambiguous figures we've come to expect in plays and movies, characters of mixed quality whom we can love even as we doubt them. Sister A. doesn't want our love: she wants obedience, perfect conduct and the fear of God, thank you very much. And her narrowness is riveting: I was so taken with Decker's performance, I felt as if I were encountering the play for the first time.

Eric Davis as Father Flynn is also superb. What we know about Flynn a few minutes into the play is that he was seen to take 12-year-old Donald Muller into the St. Nicholas church rectory for a conference, that upon his exit the boy seemed troubled, and that Sister James thought she smelled alcohol on his breath. Flynn insists that Donald was caught drinking altar wine and that their interview was on the subject; Sister Aloysius is convinced that Flynn gave the boy wine in order to molest him. Davis' job, then, is to enact this uncertainty; and he handles it cannily. Unlike Philip Seymour Hoffman in the film, he comes across as working-class, a bit of an athlete, the sort who takes pleasure not just in his soul but also in his body. Can we imagine him taking advantage of a young student? Yes, it seems possible. Can we also imagine him as guiltless? Yes, equally well. I've seen Davis on stage many times over the last few years, but this is the grittiest performance I've ever seen him give (as a priest, ironically), and it's more than satisfying.

The two other portrayals aren't quite as persuasive. As Sister James, Samantha McKinnon Brown is adequate, but she goes too far in losing her temper with Sister Aloysius, and at other times tends too much toward a sugary sweetness. Erica C. Sutherlin as Mrs. Muller has a different problem: she doesn't project the complexity of a woman who's caught in a web made of race, class and sexuality. An unqualified success, though, is Scott Cooper's fine set, on which faux-stained glass portraits of saints are hung, along with a wall-sized picture of the crucifixion. And director Olson's sound design, featuring church music between scenes, sets the play's tone very well. Adrin Erra Puente's costumes, from nuns' habits to Mrs. Muller's demure suit, could hardly be better.

And Doubt, in this production, is a fascinating play, well deserving of its Pulitzer Prize. See it in order to decide for yourself whether Father Flynn is innocent. Or see it for Christine Decker's acting as Sister Aloysius — one of the best performances on a local stage in many months. In either case — in any case — it's worth your attention.