It’s not often that an unknown, just-out-of-school playwright is introduced to New York with a full-scale production at the venerable Manhattan Theatre Club. But Liz Flahive proves that she’s worthy of the gesture with her marvelous new play “From Up Here,” which opened last night at City Center in an invigorating production by Leigh Silverman.

What is so striking about Ms. Flahive’s play — apart from its compelling characters and pitch-perfect dialogue — is the self-assurance with which she writes. Here is a young playwright with an extraordinarily clear voice, supremely confident in her movements.

The feat is all the more impressive in light of the play’s thorny subject matter: “From Up Here” is a bittersweet drama about a family in the days after one of its members, a high school junior named Kenny, has waved a gun around the school cafeteria.

Yet under the perceptive direction of Ms. Silverman, who is fast becoming one of New York’s most acclaimed directors of new work, the superb cast of “From Up Here” finds honest laughter and genuine heartache in the plight of a failed school shooter. For Kenny, as Ms. Flahive shows us, is much more than that label suggests.

Kenny (Tobias Segal) is essentially a tenderhearted kid, kind to dogs and protective of his older sister, too sensitive to cope with the brutality of teenage teasing, too nervous and shy to stand up for himself. His biochemistry doesn’t help him, either; even on a heavy dose of Paxil, he jitters constantly. As played by Mr. Segal, an astonishingly gifted young actor, Kenny is mesmerizing — he’s utterly closed off to us, yet we yearn to get closer to him.

What is liberating about “From Up Here” is that Kenny, magnetic as he is, is treated not as the star but as part of the larger constellation of his traumatized, reeling family. His mother, Grace (Julie White, using her trademark wit to dig to considerable emotional depths), is simultaneously furious, sympathetic, and terrified. Her second husband, Daniel (Brian Hutchison), already ostracized by the boy for not being his real father, finds himself with the appalling task of having to check Kenny’s backpack for sharp objects every morning. Kenny’s smart-mouthed younger sister Lauren (Aya Cash) sits with him at lunch, facing down the stares of the rest of the school. And his hippie-dippy aunt Caroline (Arija Bareikis) flies in from a 24-day Third World trek to check in on him.

Aunt Caroline is the one person Kenny trusts easily. Unfortunately, she’s never around for more than a couple of days. One of the lovely things about “From Up Here” is how gently Ms. Flahive draws the parallels between aunt and nephew, letting us glimpse their bond and their similarities without ever pressing the point.

Kenny’s other relationships emerge in the same understated, organic way. (Unlike most young writers, Ms. Flahive never forces a bud.) When his sister insists that he chaperone her on a date to the school dance, Kenny makes himself go because he genuinely likes the goofy tall kid who’s asked her out, Charlie (Will Rogers, in a scene-stealing performance). At the dance, when Charlie gives him a CD, there’s a quiet yet earthshaking moment when Kenny realizes that at least one person at the school doesn’t see him as a cold-blooded killer. Yet, wisely, Ms. Silverman underplays this, too.

Most important, and most moving, is Kenny’s bruised and broken relationship with his anguished mother. For most of the play, Kenny dances around his mother, never getting close enough to touch, and the play dances around them, too. Only in the final minutes are they forced to confront each other, alone. These scenes brim with earned emotion, as Ms. White fearlessly plumbs the depths of her character and Mr. Segal matches her, line for line.

Here, as in all the dialogue, Ms. Flahive shows a gift for melding the ordinary facts of suburban life — car keys, cordless phones, minivans — with the strong undercurrents of a family in acute distress. Her language is almost always naturalistic, often sounding throwaway, and yet every line contributes to a growing impression of a living, breathing family. (Allen Moyer’s sets, especially the lifelike kitchen, strike exactly the same tone.)

Ms. Flahive calls her play “From Up Here,” and a brief prologue and epilogue attempt to shoehorn in some mountain-climbing imagery. She needn’t have bothered: The play arrives like a gust of fresh air all on its own, a gem of a debut in a near-flawless production.

Until June 8 (131 W. 55th St., between Sixth and Seventh avenues, 212-581-1212).