Jackie (Bitsie Tulloch; pictured) is porcelain doll-fragile, her gaunt frame as rigid as her pulled-back hair. Her eyes, strewn with mascara, dance with hurt when something gets under her skin which is close to always. When her sister, Caroline (Marguerite Moreau), comes to visit her and her meek boyfriend Ryan (David Giuntoli), Caroline insists on taking them out to dinner, which turns out to be a surprise party. And when the boisterous group returns to Jackie’s house, the event transforms, with zero warning, into an intervention.

Jackie sits in stunned silence as her boyfriend, friends and sister lecture her about her supposed anorexia, promiscuity and drug use. She storms out in anger, and Ryan pursues her, but Caroline, oddly, decides to stay and entertain the rest of the gang; she clearly has ulterior motives, beyond saving her sister. As the night proceeds further into debauchery—a misguided fireworks display, a half-naked pool excursion, a suggestive dance—Caroline’s own severely destructive foibles are gradually revealed.

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Writer-director Adam Christian Clark, who makes his feature film debut, has an intriguing premise in his grasp—what if the most reckless person in your life threw you an intervention?—and for awhile, “Caroline and Jackie” bubbles with nervous, dizzying energy. Clark has definitely boned up on his Robert Altman and John Cassavetes; his camera habitually fixates on a silent character’s disconnected face as salty, vibrant small talk oozes around her, and the ensemble scenes have a loose, improvisatory feel which the actors slip into nicely. While the material certainly could have been funnier, “Caroline and Jackie” is a memorably unsettling work.

Moreau is particularly creepy, as well as agonizing, as the alternately haughty and self-degrading Caroline. Minutes after scolding Jackie relentlessly, she is nuzzling up to Jackie’s boyfriend wearing nothing but a towel. Later on, after she wades into the pool topless, we watch the entire group shift their condescending concern from Jackie to Caroline, and Moreau expertly conveys her character’s drunken embarrassment and pathetic need to be in the right; she can’t resist calling Ryan a “pervert” after he sympathetically gives her a towel.

Wisely, Clark doesn’t settle for the manipulative tactic of making the audience take sides. Long after it’s become apparent that Caroline is, at least on the surface, the bigger screw-up, Jackie still remains a selfish, impulsive character, prone to switching allegiances without reason. Most of her and Caroline’s co-dependent past is unexplained, which adds to the film’s aura of mystery.

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In fact, the major flaw with “Caroline and Jackie”—and it’s a big one—is its lack of exposition, which is impressive for awhile but finally frustrating and empty. The film ends with an out-of-left-field outburst from Jackie, and though it’s explosive and unpredictable, the director provides so little back story that we don’t understand the cause, or the meaning. Clark has made a tense, often moving film, but he hasn’t really worked out why these warped, damaged sisters even tolerate each other, let alone share a deep bond.