Anyone who has even a passing familiarity with Wallace Shawn’s plays can guess how much credence to give this statement from Mr. Smith, the rumpled protagonist of “The Music Teacher”:

Most people have always just seen me as a rather nice, rather bland fellow who was giving what he could to everyone he met and taking nothing.

Whether it’s the impressionable young woman who learns to appreciate Nazism in “Aunt Dan and Lemon” or the well-meaning professor who succumbs to pornography and lethal indifference in “The Designated Mourner,” Mr. Shawn has made an art of creating ingenuous narrators who take us by the hand and guide us into some of the more contemplative corners of hell.

“The Music Teacher,” a consistently intriguing play-opera hybrid that Mr. Shawn has co-written with his composer brother, Allen Shawn, would appear to cover similar ground, although the path is more circuitous and the pacing less surefooted this time. The placid Mr. Smith (Mark Blum), a middle-aged professor recalling a pivotal experience from when he was 30, has a tentative, almost broken quality; something has clearly gone awry. Jane (Kellie Overbey), a former star pupil of his who shares narration duties, describes Mr. Smith as “ruined-looking” at one point, and after more than two decades, the rebuilding effort still isn’t quite complete.

The two crossed paths at a small New England boarding school (conveyed hauntingly through Greg Emetaz’s understated video projections), where young Mr. Smith served as a beloved if somewhat odd mentor. Mr. Smith’s easy banter with his predominantly female students slides into questionable territory now and then, but as mapped by the shrewd director Tom Cairns, the affection between him and his class is clearly mutual.

Mr. Smith has a particular fondness for the earnest, precocious Jane, and the two decide to collaborate on an opera. This is where the Shawns and Mr. Cairns move in a curious and only partially successful direction. Allen Shawn’s music, which lands in the Samuel Barber-Charles Ives school of flinty tonality, has served as a sort of emotional underscoring thus far; now the two adults’ ruminations give way to a full-fledged re-enactment of the resulting opera (with a libretto by Wallace Shawn). The piece – a ludicrous swords-and-sandals affair packed with forbidden lockets, shadow puppets and murder-suicides – takes up the next 45 minutes or so of “The Music Teacher.”

The hothouse atmosphere of an intense collaboration, the inappropriate surgings of emotion between professor and student, the sexual untethering that stems from artistic expression – these all lend themselves to cataclysmic melodrama. And as the opera unfolds, starring the younger versions of Mr. Smith and Jane as two-thirds of its central love triangle, similar breaches seem inevitable both in the play and in the play within the play. (Wayne Hobbs and Sarah Wolfson sang the two roles beautifully at one recent press performance; these characters and one other have been double cast, as is often the case in opera.)

But the Shawns take the notion of emotional and sexual maturation through art in a curious direction: The professor, not Jane, is the one who essentially comes of age, although both will be enveloped in the chaos that follows. The opera stirs up a fury of emotions that result in Mr. Smith’s fleeing from the town and embarking on a priapic whirlwind tour of “the city.” Has he become his own virile creation? Or have his imaginative flights launched him into a sort of hypersexualized reverie? Either way, the results will have serious repercussions for both the teacher and his star pupil.

From a dramaturgical standpoint, this setup has its risks. For one thing, no matter how small or how liberal this New England town is, any high school professor who casts himself as the love interest in a student production will have some explaining to do. This becomes clearer still when the four servant girls in the chorus stare at Mr. Smith’s character and sing, “There are things we’d all like to do / That might be very pleasant / … But we can’t because they’re wrong.” What was that he was saying earlier about “giving” and “taking”?

Also, many opera singers – particularly young ones – would struggle with the intense emotional demands of Wallace Shawn’s lacerating, deceptively colloquial text. Mr. Cairns and the authors have struck upon the understandable but frequently awkward solution of entrusting Mr. Blum and Ms. Overbey with virtually all of the dramatic acting.

And the opera? Well, Allen Shawn’s music considerably overshadows his older brother’s libretto. I believe this was intentional: A professor’s contribution to the work would presumably be more polished than the florid imaginings of a precocious student. Nonetheless, for all its symbolic import and for all of Allen Shawn’s compositional gifts, the opera overstays its welcome considerably. I had my fill of the intentionally amateurish “school performances” well before Mr. Cairns appears to have, and the complex teacher-student dynamic could have been conveyed just as tellingly through a more concise telling.

The two extraordinary lead performances are crucial in offsetting this dip in intensity. Both Ms. Overbey – who captures the poised, slightly smug affect of a model student exquisitely – and Mr. Blum spike their almost wistful recollections with a distinct undercurrent of the lasting damage.Their material is devoted almost entirely to monologues, yet the complicated dynamics between the two are crystal clear. Even when “The Music Teacher”gets bogged down in its self-imposed longueurs, these two sensitive, damaged voices can be heard with a bracing clarity.

Until April 9 (18 Minetta Lane, between Bleecker and West 3rd Streets, 212-307-4100).