Longtime Scrubs star Zach Braff knows comedy, obviously. But as his much-admired 2004 movie Garden State demonstrates, Braff the writer is good at intertwining the lighter and darker moments that make up pretty much everyone’s life.

Braff’s first play, All New People, is getting its regional theater debut in a Zoetic Stage production at the Arsht Center’s cozy Carnival Studio Theater. Staged by Stuart Meltzer with a sensitivity toward the ebb and flow of the characters’ many moods, the play careens from being riotously funny to sobering, sometimes within the space of a few minutes. And yet again, Zoetic provides a showcase for some of South Florida’s finest acting talent.

All New People swirls around Charlie (Nicholas Richberg), its depressed protagonist. When we meet him, he’s summoning the courage to step off the bar at a swanky Jersey Shore beach house and let the noose around his neck take him to a place of permanent darkness.

But on this wintry day, something -- God or fate or happenstance -- intervenes. Three strangers show up to change the course of Charlie’s death. Or, more significantly, his life.

First on the scene is Emma (Amy McKenna), a British realtor who lacks a green card but can’t go home. Then comes Myron (Todd Allen Durkin), a firefighter, drug dealer and former drama teacher who’s sweet on Emma. He, too, is where he is because of a ruinously bad decision. Finally Charlie gets a “gift” from his wealthy pal who owns the beach house: Kim (Betsy Graver), a bubbly high-end escort who will do whatever it takes to cheer Charlie up.

In All New People, Braff explores loneliness and the crutches people use (drugs, booze, sex and the like) to feel less lonely. His writing is sharply observant, sometimes blisteringly funny, though elements of the back stories he gives the characters are hard to buy. Black-and-white videos illuminate each person’s story, with Christopher Demos-Brown featured as a British thug, Kim St. Leon as a disgusted high school principal and Scott Douglas Wilson as Charlie’s buddy.

Certain production elements could use tinkering. Michael McKeever’s beach house is a sleek playground for the four characters, but the swirling “snow” supplied by lighting designer Luke Klingberg can’t disguise the fact that there’s nothing but a curtain outside the front door. On opening night, the images and sound in the first couple of videos were out of synch (the later ones were fine). Charlie’s way-loose noose looks flimsy and harmless. McKenna wears pants with front pockets that bulge out (though she isn’t heavy in the least), and Graver is dressed more like a Vegas streetwalker than an elegant escort.

What needs no work whatsoever are four terrific performances.

Richberg’s task is the toughest one, as Charlie is often an emotionally switched off observer. But the final moments of his journey back toward light and life are lovely. McKenna is totally believable as the chatty, drug-loving Emma, yet it’s clear that every intricate element of her performance has been effectively thought out. Graver delivers one of the best performances of her young career, making Kim an irresistible life force. And Magic City regular Durkin crafts yet another magnetic character: funny, outrageous and, when Myron incongruously delivers one of Shylock’s speeches from The Merchant of Venice, leaping from laughter to moving drama in a heartbeat.

This quartet of actors is the play’s greatest asset, and watching them work is the greatest pleasure of All New People.