The Walnut Street Theatre fits one serious contemporary play into each season of musicals and crowd-pleasers, and David Lindsay-Abaire?s 2011 Broadway hit Good People fills that role this time around. While definitely a comedy, Good People explores class in America (defined somewhat by race and accent, but mainly by income) with discomforting insight.ÿ

This co-production with Lancaster?s Fulton Theatre features Julie Czarnecki?s strong turn as Margie, a lifelong resident of Boston?s Southie neighborhood. Goodhearted and proud, she?s raised a disabled daughter alone by working low-level jobs, but loses her Dollar Store gig due to frequent lateness. Boss Stevie (Jared McLenigan) is an old classmate?s son. Everyone knows everybody in Southie.ÿ

Desperate for work, pressured by landlord Dottie (Sharon Alexander) and egged on by bestie Jean (Denise Whelan), Margie approaches old boyfriend Mike (Dan Olmstead), a successful doctor living in posh Chestnut Hill, to hook her up. When Margie calls him ?lace-curtain Irish,? a derogatory term for a roots-denying snob, Mike invites Margie to his home to prove her wrong.ÿ

The inevitable clash of Mike and Margie?s Southie origins and his wealthy, cultured life amuses, but Bernard Havard?s astute production keeps Lindsay-Abaire?s serious themes foremost. Czarnecki fully realizes Margie?s complexity, revealing a woman smart enough to know that disparate fortunes stem more from luck than brains. She?s a fuming mixture of desperation and hope, and can?t contain her seething resentment. ?How?s the wine?? Mike?s wife, deliciously played by Danielle Hebert, asks. Margie replies, ?How the fuck should I know?? her sarcasm tinged with helplessness.

?You gotta be a selfish prick to get anywhere,? Jean remarks. Mike certainly qualifies, but Olmstead?s nuanced performance shows that he doesn?t know how selfish, or how lucky, he?s been.ÿ

Jacob Mishler?s song choices are the production?s only misstep, with tunes like ?Fight the Power? and ?Had a Bad Day? cutely echoing the obvious. Good People is better served by Robert Klingelhoefer?s slick set and Shon Causer?s sharp lighting, neatly showing the distance between Southie?s gloomy squalor and the light-infused luxury Margie may never know.

Through April 28, $10-$85, 825 Walnut St., 215-574-3550, walnutstreettheatre.org.ÿ