Moxie is a slang word meaning vigor, pep, courage or nerve. The word came from Moxie, originally created in 1876 in Lowell, Mass. as a patent medicine elixir said to reinvigorate those who downed a teaspoon or two. When soft drinks became popular, Moxie’s formula changed (1884) and it became a soft drink that enjoyed popularity until the 1920s and is still available today. There is even an annual Moxie Festival in Lisbon Falls, Maine, pop. 4,000-plus. Founded in 2004, San Diego’s Moxie Theatre exemplifies moxie, the word descended from Moxie. Among the city’s gypsy theater companies it provides a piquant elixir bound to invigorate. The current production, to be seen at Diversionary Theatre through March 8, is no exception. Written when she was a mere 22 years old, Lucy Prebble’s “The Sugar Syndrome” is bracing, funny and dark, taking audiences to the secret places in four damaged people. The protagonist is Dani, a 17-year-old anorexic recently released from institutional rehabilitation (an incisive performance by Rachael VanWormer). Dani’s dallying father is entirely absent, and Jan, her neurotic mom (excellent Terri Park), tries to cut the crotch from his trousers with blunt scissors — there’s a metaphor for you. Looking for excitement, dominance and approval, Dani meets up with men on line. Then she meets up with two of them in reality. The most terrifying is a pedophile named Tim (Sean Cox, brilliant), who awaits Dani thinking he’s meeting an 11-year-old boy. Tim is intelligent, nurturing and gentle and appears truly to be working on his problem, even though he admits the aversion therapy didn’t work. Prebble thus humanizes the most despicable male of the species, whom the empathetic Dani treats with great kindness. Under his surface ineptness, an insecure geek named Lewis (Jesse Allen Moore) has more volatility and potential for danger than Tim. All the acting is excellent, but at its core the play belongs to Dani and Tim, who develop quite a bond in their brief scenes together. In many ways, Tim becomes Dani’s father — a rather scary prospect, that. Eventually, fearing a possibly imminent visit from the police, Tim entrusts all he really is, including his vulnerability, to Dani. The other two roles are more stereotypes than characters: Lewis symbolic of apparently benign, sexually frustrated young males; and Jan, powerless midlife women who never develop talent or identity outside their husband’s sphere and suddenly find themselves dumped. Nonetheless, it’s a stunning first play from a young British woman who as a result of the play’s success was given her own television series. Despite its ability to hold up a societal mirror to four challenged characters and give onlookers a few laughs in the bargain, the play is dissatisfying in retrospect. Perhaps a larger audience than that of the matinee performance Feb. 22 would change that feeling. Director Jennifer Eve Thorn does some of her best work upon Amy Chini’s spare and adaptable set, lighted effectively by Mia Bane Jacobs. Jo Anne Glover is costume designer, Rachel Le Vine, sound designer. Performances are at 8 p.m. Wednesday through Saturday and 2 p.m. Sunday through March 8 at Diversionary Theatre, 4545 Park Blvd., San Diego. For tickets and information, visit www.moxietheatre.com or call (858) 598-7620.