Florida Fandango is a 16-year-old girl who is accused of killing her mother because she is attractive and sexually curious and is therefore a figure of suspicion in today’s society. That’s the premise of the opera “Florida,” among the most ambitious ventures I’ve seen from the company UrbanArias, which gave the piece its world premiere Saturday night at the Atlas.

UrbanArias specializes in recent works (written in the past 50 years or so) and usually in short works, which Florida is not: Rare for this company, it has two acts and lasted about two hours. The score, approachable and rife with overtones of jazz and musical theater, is by Randall Eng, and it calls for considerable forces: a cast of seven singers, plus 17 members of the Inscape chamber orchestra, the company’s regular collaborator, spread out behind the suburban redwood deck of Andrew Boyce’s set.

The libretto, by Donna Di Novelli, is at once moderately amusing and consistently opaque. We’re not quite sure how Florida’s mother dies, even though the murder is the climactic scene of the first act, and we’re not quite sure what happens in the second act, which takes Florida through her trial, her mother through her autopsy, and Florida’s sometime boyfriend Marc through a half-confession and his marriage to a woman who began writing him in jail.

“Florida” certainly had strong moments, not least Florida herself: Sharin Apostolou was terrific playing a curious, vibrant teenager with a vivid and seemingly tireless soprano voice. Some of the character drawing of Florida is evocative. The idea of a scream inside that, for lack of a better outlet, translates into bright nail polish and blood-red lips; or the number “Madly in Love,” about being in love with nobody in particular, speak strongly to the teen female experience.

And the casting was generally good. One of the piece’s hallmarks are the nosy neighbors, the Redwoods, owner of the deck and observers and judges of the goings-on at Florida’s house, sanctimonious and clueless and ultimately affected by the aftermath of the murder: Ethan Greene was particularly strong as the “Redwood Male,” while Ian McEuen offered a firm, darkening tenor and a range of brief, vivid characterizations in several smaller roles, from the Redwood son to a cop. Nancy Allen Lundy offered a thin wiry voice and strong characterization as the flaky mother, who continues to be a force onstage even after her death.

But the piece as a whole suffered from its lack of clarity and loss of dramatic arc in the muddy not-quite-procedural of the second act. Eng’s lyrical and often dramatic music, energetically led by UrbanArias’s founder, Robert Wood, wasn’t enough to give shape to a plot in which a lot had to be inferred, teased out from between Di Novelli’s poetic but abstract lines. At the end, the cast belted out the refrain, like a moral, “Who seduced you?” adding, “Sexual tension resides under it all.” It was a summation of a plot that never quite delivered the goods, and an evening that spent a little too long trying.

“Florida” has two more performances, on April 13 and 14 at the Atlas Performing Arts Center.