Theresa Rebeck’s remarkable new drama, Dig, which opened Wednesday at Primary Stages’ 59E59 Theaters space, is a big-hearted look at some very troubled souls, people who resist easy characterization or casual dismissal. The action centers on Roger (Jeffrey Bean), the middle-aged owner of a struggling plant store somewhere in suburban middle-class Ohio, and Megan (Andrea Syglowski), the emotionally wrecked 36-year-old daughter of Roger’s part-time bookkeeper who has returned home after a prison stint following the death of her son (left in a 110-degree car in summertime).

Where Roger is almost hermetic in his isolation in his shop (hyperrealistically rendered by designers Christopher and Justin Swader), content to repot African violets and prune overgrown shrubs while maintaining a strict protocol about the shop’s hours of operation, Megan is a live wire whose trauma remains so close to the surface that it explodes outright at the slightest provocation. Early on, encountering a kindly suburban customer (Mary Bacon) who suddenly recognizes Megan and her very public court case, Megan lashes out with such disproportional venom that it’s startling.

Over time, working an unpaid job as Roger’s assistant, she begins to calm down, absorbing the language of AA and the rigor of truth-telling as a means of building a routine for herself and a distraction from her troubled past. Her widowed adoptive father (Triney Sandoval) and a babbling stoner co-worker (Greg Keller) offer similarly complicated counterpoints, speaking their own blinkered truths about Megan’s evolution. Dad is unable to fully trust her, or to forget the damage she has wreaked (including to his finances), while Keller’s Everett is a slackerly dude who rightly sees Megan as a PR nightmare that could finally sink the store — as well as a woman with enticing bad-girl appeal.

The cast sketch these characters as believable, well-rounded individuals — neither saints nor sinners past the point of redemption or growth. While Syglowski astonishes in the showier role, a bundle of raw nerves ready to snap at the drop of a flower petal, Bean provides a necessary ballast with his almost preternatural calm and watchful gaze. Rebeck’s direction, like her writing, is sharp and humanistic, if at times overemphatic. In early scenes, Bacon’s Christian prayer-group-goer seems more like a sitcom trope, and Roger’s language can lean too heavily on horticulture metaphors about how to nurture the best outcomes in his leafy charges. (I also wish that at least some of the flowerpots angrily swept off store counters had actually broken — surely this suburban shop doesn’t just sell plastic pots.)

But these are quibbles. Rebeck’s characters are drawn with an unusual degree of honesty, perhaps most when they are so clearly lying to themselves. “I think the theory is that if you make the truth your friend it can’t just suddenly come at you and eat you alive,” Megan says early on, but her journey toward self-acceptance follows a convincingly jagged trajectory. A fraught encounter with her ex-husband (David Mason, perfectly squirrelly), another bundle of contradictions who wears his discomfort like a uniform, only makes matters worse — reinforcing a sense of guilt that she fears no amount of apologies or meetings or affirmations will ever dispel.

All that messiness allows us to swallow some unexpected plot developments, particularly in the two-hour play’s eventful second act. But the messiness is the point. As is the declarative truth-telling, an outgrowth of AA and other self-help treatment that calls for public declarations of feelings and acknowledgements of shortcomings. Dig goes directly to the root of our humanity, the truths we’re willing to share with each other as well as the ones we dare not speak, even to ourselves. It’s a new American classic.