St. Louis audiences are the first to see "Falling," Deanna Jent's new play about a family living with the struggles of autism.

Bet that we won't be the last.

Jent's drama — inspired by her 17-year-old autistic son and her family's day-to-day life in the vortex of what she calls "extreme parenting" — is a gripping piece of theater, emotionally wrenching and theatrically astute. It has, as they say, legs. It also has a keen mind and a warm, though troubled, heart.

Jent, who is artistic director of Mustard Seed, and Lori Adams, the director of the play, plunge us straight into the "ordinary" life of this anything-but-ordinary family. "Falling" opens in the cozy Martin house (affectionately designed by John C. Stark) where everyone's getting ready for school or work. But along with the comfy sofa and computer desk, the living room features an odd touch: a box of feathers set high on the wall, with a cord attached to it.

The father, Bill Martin (Greg Johnston), has rigged it up so that the teenage son, Josh (Jonathan Foster, in a riveting performance), can release the shower of feathers, rocking from side to side under its gentle fall. It makes him happy and calm.

It also makes a mess, but so what. In its exhausting first minutes, "Falling" gives us a glimpse of a family where moments of calm are rare and unlikely to last. When Bill's mother, Sue (Carmen Russell), comes for her first visit in a while, we see through her loving but appalled eyes how people may get used to life on a precipice.

Anything from the arrival of the school bus to the sound of the blender might precipitate a crisis. The Martins cope with rituals, rewards and code words, but now that Josh is bigger than his mother, Tami (Michelle Hand), and sister, Lisa (Katie Donnelly), the family lives in constant dread of his tantrums. But what are their alternatives? If they knew, they'd certainly try them.

Lisa, whom Donnelly turns into the wonderful embodiment of eye-rolling adolescence, is fed up — the usual teenage condition, but with way more justification. Sue believes in the power of prayer — something that, the parents acknowledge, might help them, even if it hasn't so far. (Russell's performance, rooted in Jent's thoughtful writing, never mocks Sue's sincere beliefs.) Johnston, a veteran of the St. Louis stage, does his best work ever as Bill, a man just trying to keep his family on an even keel. Or is he actually trying to keep his emotional distance?

That's what Tami sometimes suspects. Michelle Hand makes Tami tight as a drum, physically turning in on herself. When Bill tries to embrace her, she almost shudders; when she's at the computer, she hunches her shoulders as if she expects an attack to come from behind. She's exhausted, and she's not a saint. But she's one of the fullest creations we're likely to see on stage, particularly in a brand-new play.

Many people with autism are not nearly so disabled as Josh; on the other hand, some theatergoers with experience in this area may find him too communicative. But "Falling" is a play, not a case history, and the details of his circumstances have been shaped to suit the stage.

That in itself says something important about "Falling." It's not a plea for a cure, or for better treatment, or for sympathy. It's both simpler and more complicated than that. Like many other plays ("Awake and Sing!" "A Thousand Clowns," "The Three Sisters"), it's a thoughtful portrait of a family struggling to hold on in particular and challenging circumstances. You don't want to miss it, and you shouldn't have to. Since Mustard Seed announced "Falling," interest has been so strong that the run, originally set to end Sept. 11, has been extended for a week.

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"Falling"

Who Mustard Seed Theatre at Fontbonne • When Through Sept. 18. 8 p.m. Thursdays-Saturdays, 2 p.m. Sundays • Where Fontbonne University Fine Arts Theatre, 6800 Wydown Boulevard • How much $25; $20 for students and older adults • More info 314-719-8060; mustardseedtheatre.com