NEW YORK, NY.- Hiring a babysitter is a high-stakes leap of faith. How well can you really know someone before trusting them with your kids? And what’s going to happen when you’re not at home? Maybe she won’t quite be Mary Poppins, but let’s hope the glint in her eye doesn’t remind you of the unassuming villain in a psychological thriller.

With her Pre-Raphaelite curls, plinking bangles and wide-eyed smile, the candidate who sweeps through the door in “Lucy,” which opened at the Minetta Lane Theater on Monday night, appears closer to the former ideal. Ashling (she’s distantly Irish) calls herself a career nanny with 40 years of experience, despite seeming not quite as old herself. Played with a sly incandescence by Lynn Collins, Ashling colors her speech with generous emphasis, insisting that child care keeps her young and that she considers her role on par with a co-parent.

The client, Mary, looks like she could give birth at any minute, and has let her search for help come down to the wire. Played with delicate, white-knuckled composure by Brooke Bloom, Mary is an overworked radiologist and single mother with a 6-year-old daughter (Lucy, for whom the play is named) and a son on the way. She is the sort of tightly wound person motherhood has only somewhat unraveled; when she offers Ashling the job, it comes with a stack of guidelines as thick as a novella.

Written and directed by Erica Schmidt, “Lucy” is seamlessly layered, extraordinarily entertaining and tricky to classify. A cleverly detailed exploration of child care as both a kind of labor and a primal instinct, it is a workplace comedy set at home, where boundaries are porous and personal stakes are exceedingly high. When Mary discovers, for example, that she can smell Ashling’s perfume on her infant son at night, it feels like an intimate intrusion. But when Mary awkwardly confronts her, Ashling is breezily evasive.

“Lucy” is also an irresistible, engrossing slow burn, as tension between the two builds under pressure. Laughs increasingly double as sighs of relief as the suspense of discovery escalates through the show’s taut two-hour running time. Mary is undoubtedly a micromanager. Ashling, meanwhile, relishes her freedom, reminding Mary of what she has sacrificed to become a mother. And although Ashling’s strangeness is undeniable, it’s also slippery to pin down. The most telling clues may come from Lucy (Charlotte Surak, adorable), but how reliable can a young child be?

Schmidt, who recently adapted “Cyrano” into a stage musical and whose play “Mac Beth” recast Shakespearean tragedy among vicious high schoolers, has a way of uncovering and magnifying the profundity simmering underneath everyday conflict. On the surface, “Lucy” is a tug-of-war between opposing personalities. At its core, it confronts questions of power, possibility and human nature.

Schmidt’s staging, produced by Audible, is a crisply orchestrated slice of Manhattan life, impeccably designed to reveal her precisely drawn characters. The tasteful austerity of Mary’s open-plan kitchen-living room aptly reflects her strict minimalism, as does her understated, mostly black wardrobe (the set is by Amy Rubin and costumes by Kaye Voyce). Cha See’s dynamic lighting underscores the play’s subtly eerie shifts in mood, and there’s unexpected humor in the music from sound designer Justin Ellington (perhaps a nod to the play’s future release as an audio play).

“Lucy” is also a kind of inventory of the roles women are expected to play, whether they become mothers or not, and the systems that assign value to them accordingly. That draws even more attention to the fact that Bloom and Collins hardly seem to be playing roles at all; the actors are so thoroughly committed and convincing that any hint that things may not be as they seem feels all the more destabilizing. It’s the sort of feeling that might arise after trusting your life to someone else’s hands and then realizing they’re a total stranger.

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‘Lucy’

Through Feb. 25 at the Minetta Lane Theater, Manhattan; lucytheplay.com. Running time: 1 hour 50 minutes.

This article originally appeared in The New York Times.