Billy, charming Billy—Londoner, younger son, smile so sweet you don’t register how much it warms the room until, in Act 2, it’s gone. Actor Joey Caverly anchors Nina Raine’s Tribes, onstage at Studio Theatre, with a performance of surpassing sensitivity, a still, centered presence amid the play’s whirlwind of words.

Which, it’s important to note, he can’t hear. Character and actor alike are deaf; Tribes is the story of Billy’s coming to terms with his hearing family, or more accurately the tale of his setting new terms for them. Raised to lip-read rather than sign and kept at a distance from the deaf community by his hyperarticulate, abrasively intellectual parents on the theory that disability culture is marginalized culture, Billy has a foot in two worlds and a home in neither. What becomes of him, as he falls for a woman who opens new doors for him, and as he discovers how marginal he’s been even in the lives of those who love him, is wrenching enough on the page; Caverly, in an arc that takes him from gentle to clenched to wrathful to tears, makes it downright heartbreaking.

That girlfriend, played with a fawn’s skittishness by Helen Cespedes, is the child of deaf parents, now losing her own hearing—and, in a sense, a part of her personality. (Sign language, she notes, can be a painfully blunt mode of communication; will she become a coarser person as her hearing goes, she wonders?) Her changing circumstances change Billy, inevitably, and because she likes his family, and they her, she’ll eventually end up in the terrible position of being both the unintentional catalyst for his alienation from them and the translator who’ll have to tell them why.

And oh, that family. Michael Tolaydo’s brutally intelligent paterfamilias, learned and principled and lamentably unwise. Opposite him, Nancy Robinette’s aspiring novelist, warmer but no less waspish when provoked. A sister and brother, one (Annie Funke) convinced she’s the family’s runt and one (Richard Gallagher) plagued by the voices in his head. Billy, sweet sensible Billy, is the only one who really connects with all of his relations—until he realizes, as he puts it, that he’s been little more than the family mascot.

What we say, what we hear, what we intuit, what tone and body language convey, what a look can say in silence—these are the texts and subtexts of Raine’s wonderfully expressive play, a language drama that unfolds in at least three tongues. (And, in David Muse’s fluid, fluent production, in the wonderfully apt projections, designed by Erik Trester, that play like water on the walls of Wilson Chin’s cluttered, homey apartment set.) The story of Billy and his fractious clan is the story of a life on the border of communities, yes—and the story of everyone who’s ever wondered whether they belong.