Small theater companies usually find clever ways to artfully suggest scenic elements onstage. Not so with Underdog Theatre's production of "Luna Gale," a drama about meth-addicted new parents that had its Twin Cities premiere last weekend at Southern Theater.

Don't be put off by the cut-rate set — a space demarcated by moving cartons and file boxes that looks cluttered and clunky, but extends metaphors in the play. Underdog, the feisty company founded by wave-making theater artist Kory LaQuess Pullam, has tapped director H. Adam Harris for a poignant staging by a crackerjack cast.

Rebecca Gilman's 2014 play (whose title echoes the baby's name) lands at the intersection of the meth epidemic, the foster-care crisis and evangelical Christianity. Young, unemployed meth users Karlie (Briana Patnode) and Peter (Pullam) are parents of a neglected infant. Social worker Caroline (Jodi Kellogg) steps in to help, giving temporary custody to Karlie's mother, Cindy (Megan Kelly Hubbell), a deeply religious woman who is anxiously awaiting the rapture.

After Cindy petitions to revoke her daughter's parental rights, Caroline has second thoughts about her custodial decision. Meanwhile, Caroline's boss (James Rodriguez), who holds a secret agenda, has his own idea about how the case should be handled.

Gilman's twisty plot is full of surprises. But the play struggles for focus. Is it about the child caught in a storm of dysfunction? Or is it about a social worker with her own traumatic back story?

Director Harris doesn't clarify that question, but his production has evocative moments, including a scene in Caroline's office in which her boss and Cindy's pastor (Dario Tangelson) lead a prayer. As they stand over Caroline, the social worker's eyes burn with loathing. Kellogg plays the character as both commanding and caring, with a wellspring of empathy behind her officious demeanor. Patnode's honesty elicits sympathy as does Pullam, whose end-of-show dialogue is a tear-jerker.

The ensemble is rounded out by Hubbell's zealously blind Cindy, Rodriguez's secretive boss, Tangelson's seemingly benevolent holy man and Imani Vaughn-Jones' tragic Lourdes, a girl who aged out of foster care under Caroline's guidance. Their performances, in a play that speaks to our moment, give "Luna Gale" its emotive force.