Actors like to be liked or hated. Playing the irresistibly darling Rosalind in "As You Like It" is good. And playing the heart-stoppingly evil title character in "Richard III" also is good.

But playing a big role that is neither darling nor dastardly takes a special sort of gumption. As Sister Aloysius in Taproot Theatre's production of "Doubt," Pam Nolte musters that essential gumption. Her performance is compelling. It has the fascination of watching, in slow motion, a dangerous collision. Sister Aloysius collides with Father Flynn.

Sister is the principal of St. Bernard's parochial school in the Bronx. The year is 1964. Sister wears a traditional black habit. She looks and sounds a bit like a scolding crow. Indeed, when her nemesis, Father Flynn, assistant pastor at St. Bernard's, shouts angry words at a squawking crow in the rectory garden, you know the true object of his anger.

Sister is convinced that Father Flynn is sexually abusing a boy in the eighth grade. She has suspicions but no proof. Yet she is determined to drive the priest out of St. Bernard's. She acts like a detective or district attorney whose ego demands a conviction -- no matter what.

Since it premiered in 2004, "Doubt" has become one of the most celebrated dramas of the past 10 years. It won a Pulitzer Prize for its author, John Patrick Shanley, and Seattle Rep staged a superb production in 2006. "Doubt" has ridden the wave of intense interest created by recent legal cases in which Roman Catholic priests have been convicted of abusing children. More important, "Doubt" is a thriller, an adult thriller driven by ambiguity, ambivalence and, yes, doubt. It respects an audience's grown-up capacity to savor uncertainty.

As drama, "Doubt" is precision engineered. But as an ethical inquiry, it is not at all tidy.

Faith Russell as the allegedly abused boy's mother gives definition to blurry notions of right and wrong, virtue and sin. Her son has been persecuted by peers and by his own father. He is not macho. He flourishes as a result of Father Flynn's attention. Unproven accusations of misconduct are mere meanness according to his mother. Russell conveys both timidity and courage. She touchingly expresses gratitude toward the priest and fear that Sister's inquisition will destroy what she sees as a blessing.

As Father Flynn, William Kumma is humane when secure and scrappy when under attack. Jesse Notehelfer plays a hapless young nun. Sister abuses her in a way that is similar to Father Flynn's alleged abuse of the eighth-grader. Notehelfer's character goes from happy and spontaneous to depressed and repressed. The cause of this transformation is Sister's barrage of faultfinding. Once demoralized, the young nun will do anything to gain Sister's approval. That means spying on Father Flynn.

What the facts of the abuse case are is not clear. What is certain, however, is that Pam Nolte does an excellent job of depicting a sinister fanatic, the familiar type whose purported devotion to virtue degenerates into heedless willfulness.

"Doubt" runs through April 26 at Taproot Theatre, 204 N. 85th St. Tickets $26-$33, $2 discount for students and seniors, $25 and under $15, university night (April 3) and high school night (April 9) $10 for students; 206-781-9707 or taproottheatre.org.