Can great art redeem terrible behavior? What moral responsibilities do artists have to their subjects and colleagues, particularly when those include people they ostensibly care about, or even love?

These are questions that have long inspired writers of all forms, and a tremendously entertaining and moving product of that inspiration is now on tap off-Broadway, where Jordan Seavey’s “The Seven Year Disappear” is having its world premiere. Mr. Seavey, whose previous plays include the critically acclaimed “Homos, or Everyone in America,” focuses here on the relationship between a middle-aged performance artist named Miriam and her long-suffering son and manager, Naphtali.

While this one-act piece calls for only two actors, the one playing Miriam is required to summon a number of disparate characters as the story of mother and son is essentially revealed through performance art. Happily, that assignment falls to Cynthia Nixon, who over the course of 90 minutes will, under Scott Elliott’s expert direction, delight and terrify you in one of the sharpest, funniest, and most poignant juggling acts you’ll likely ever witness.  

In Miriam alone, Mr. Seavey gives the star plenty to dig into. Pathologically controlling and impervious to the burdens she places on others — the play’s title refers to a period when she vanishes and hides, leaving even Naphtali no clue to her whereabouts — this diva seems more preoccupied by an imagined rivalry with Marina Abramović than any personal responsibilities. (“Such a hypocrite,” Miriam sneers early on of the real artist, who has no children, inserting an expletive; she quickly adds, “I mean I love Marina.”)

But Miriam does adore and worry about her son, in her fashion, calling him “my sweet boychik” — she’s a passionate convert to Judaism, we’ll learn, and has also been diagnosed as manic-depressive — and urging him to stay sober and use condoms. Naphtali, played by the rising stage and screen actor Taylor Trensch, is gay, and prone to substance abuse, though Miriam seems predictably oblivious to her impact on the latter issue.

Mr. Trensch’s Naphtali is sensitive and patently damaged, but no shrinking violet. As his exchanges with Miriam become increasingly confrontational, his repressed resentment and pain grow in intensity; and in scenes involving other characters, which seem to unfold in reverse chronological order, the actor matches his co-star in presence and wit, so that their portraits achieve a crackling synergy.

Those other characters include Miriam’s ex-manager and erstwhile lover, who is bisexual and also takes a fancy to Naphtali; a self-involved but breathlessly empathetic actress; a tragically hip teenage art student; and two other men who prove intrigued by Miriam’s son — one vaguely predatory, one disturbingly so. Ms. Nixon makes these figures by turns hilarious, creepy, and endearing, never stooping to caricature but rather finding humor and truth, however unsettling, in all of them.

Both Ms. Nixon and Mr. Trensch are costumed, by Qween Jean, in basic black against Scott Derek McLane’s stark, stylish set; props such as standing microphones conspire with John Narun’s vivid, sometimes jarring projection design to reflect a shuttling between Miriam’s conversations with Naphtali and replications or simulations of previous experiences. Naphtali observes that his mother’s work deals with time, space, and reality, musing, “Your project asks if there even is such a thing as reality.”

That work, and Miriam’s obsession with it, plainly exact far too heavy a price on Naphtali. Still, Mr. Seavey’s exquisite writing and the actors’ blazing, refined performances will pique both your curiosity and your compassion throughout.