‘Bright Star’ review: Steve Martin’s musical enchants

It doesn’t shy away from the cornball or the unapologetically sentimental. And, yes, the plot is implausibly romantic and hinged on coincidence.

Along with all that, however, “Bright Star” is also downright wonderful — a multichambered sweetheart of an original that Steve Martin and Edie Brickell created for Broadway from little more than a 1902 news item about a lost baby and an unbridled love of American roots music.

Boiled down to basics, this is the story of Alice Murphy (the extraordinary Carmen Cusack), a young free spirit in the rural South in the 1920s, and the circumstances that, two decades later, have turned her into a scary-smart literary editor of an important journal for Southern writers. But the bluegrass musical, co-created by the Grammy-winning team of composer Martin (former wild-and-crazy guy and accomplished playwright) and lyricist Brickell (offbeat and folky singer-songwriter) is propelled by many more moving parts than just one woman’s journey from heartbreak to happiness.

For starters, all the characters in the overlapping ’20s and ’40s segments are richly developed without a hint of big-city patronization. There’s not a bumpkin or cardboard villain in the lot, not even the wealthy mayor who stops his son (Paul Alexander Nolan) from marrying Alice in the most unimaginably cruel way. Odder still, almost everyone reads and talks about good books.

This is a show that creeps up on you, two seemingly simple plots that weave back and forth in time, one about young Alice and the other about young Billy (A.J. Shively), who returns from World War II with a dream of writing short stories. At first, all the “sun’s gonna shine” and “a man’s gotta do” songs seem awfully simple and self-explanatory. And designer Eugene Lee’s central A-frame cabin, which holds much of the splendid bluegrass orchestra, gets lugged around until we worry about motion sickness.

But as the relationships deepen and darken, the show — directed with a lack of cynicism and lots of rolling wood furniture by Walter Bobbie (“Chicago”) — grows with the complexity of a juicy short story. The large cast is uniformly appealing, with choreography that brings a haunting moodiness to the square dances and jitterbugs.

Then there’s the score, which builds with rhythmic surprises, melodic complexity and the deep satisfaction of humming and plucking strings. In the late ’70s, Martin’s stand-up included a “nonconformist oath,” in which he promised to be different. Promise fulfilled.