I listened to an LA Theater Works production of this 1979 play, which I had seen twice in theaters, and I also saw the film version with Meg Tilly and Anne Bancroft, and I recommend you see it, one way or the other. Then-actor John Pielmeier was inspired to write the play based on an actual case that he followed in 1977.
The events of the play are compelling, and pretty sensational. A novice nun at a convent is found bleeding in her bed, with her dead baby in a wastebasket. Initially she has no recall of even being pregnant, she says; nor does she recall the birth. The set is almost bare; almost all of the play is a series of conversations between the three main actors: Agnes, a psychiatrist and the Mother Superior. Is she a victim? Is she a murderer? Is she a kind of abused saint?
Given what has happened in the worldwide Roman Catholic Church in the last few decades, the playwright may have changed the emphasis of the play, but this is a powerful drama that touches on Agnes's reclusive and abusive (home) upbringing and her continuing struggles. She's engagingly spiritual, if tormented.
Okay, none of the characters finally seem like they actually quite fit their assigned roles--if you are going to apply realism to an assessment of them it is unlikely Agnes would have even been admitted to the convent; the Mother Superior doesn't seem like she is the way I expect Mother Superiors to operate, and the psychiatrist would seem to be violate psychiatric standards for practice, especially with the hypnosis, but hey, this is still a great play, great dialogue and wrestling with spiritual issues, with three terrific roles for women. Really mesmerizing.