"Days of Heaven, the Shakers, and the wheat fields of the Great Plains" seem unlikely inspirations for a designer as urban as born-and-bred New Yorker Zac Posen. But there they were, staring up from the front page of his program notes. So it was with an elevated level of curiosity that his audience members—at least the ones there to conduct business; Posen has many boldface pals—awaited the beginning of his show.

First up was a long black vest with pants and a white shirt, accessorized with a wide-brimmed straw hat perched atop the model's head; it was followed by a halter dress with diagonal tiers of pleats and ruffles. Not such foreign territory for Posen, whose twin talents for tailoring and dramatic eveningwear are well documented in the celebrity weeklies. What was new was the big-sky romance of a white prairie dress rethought as a fitted gown; it had a softness that Posen's more overtly sexy work lacks.

By the end, though, he had strayed into dangerous pastures. He closed the show with five dresses—four of them long or extra-long; one strapless, short, and bubble-hemmed—that were as poufy as storm-whipped clouds. These were more than a little showy, a country no-no. The Shakers, after all, didn't believe in elaborate details or added decoration. Six-foot trains are one thing, but those staffs of wheat rendered in rhinestones were an inexcusably literal interpretation of the designer's chosen theme.