La Posada Magica / SOUTH COAST REPERTORY, COSTA MESA

The “magic” of Christmas is one of the season’s most oversold commodities, but now and then Christmas believers can find the real thing.

South Coast Repertory’s seventh annual staging of Octavio Solis’ family holiday play, “La Posada Magica”--unpretentious, deliberately homespun--is just that.

Based on the Latin American tradition of neighborhood candlelight processions reenacting Mary and Joseph’s search for refuge in Bethlehem, “La Posada Magica” mixes humor and Marcos Loya’s stirring music with the story of a teenage girl whose faith in the spirit of Christmas has been shattered because her beloved baby brother died.

Unwillingly caught up in her neighbors’ posada on Christmas Eve, Gracie (Tiffany Ellen Solano) is intent only on spreading her bitterness. She succeeds in separating the group but re-encounters pregnant Mariluz (Teresa Velarde) and her husband, Jose Cruz (Sal Lopez). They need her help: Mariluz is in labor and all of the strangely transformed town’s windows and doors are closed to them.

Why are the buildings so humble, and where are the lights, the cars? (Cliff Faulkner’s set design, with painted wooden-plank flooring and starry swaths of blue and purple fabric, is spare but expressive; Don Guy’s evocative lighting is a vital component.)

This posada, it seems, with angel wings and ghoulish dark spirits--Sol Castillo and Benito Martinez--trying to tempt Gracie to repudiate life, has become reality.

The cast is a treat. While Gracie’s anger is one-note, Solano provides dimension in the lovely clarity of her singing voice. Armando Duran is a strong, anchoring presence as the wise and dignified posada leader; Castillo shines as a goofy delinquent who does a dynamite Santa blues solo. Denise Blasor and Carla Jimenez are hilarious in dual roles as chocolate-guzzling cronies and smug twin Spanish widows from “Barthelona.”

As directed by Diane Rodriguez, the play’s familial informality, with sing-alongs, remarks to the audience and dynamic onstage musicians--Loya with Lorenzo Martinez and Benito Martinez--gives way to a deepening resonance, making its own unexpected, uplifting journey.

* 600 Town Center Drive, Costa Mesa, Tuesdays through Fridays, 8 p.m.; Saturdays, 3 and 8 p.m.; Sundays, 12:30 and 4:30 p.m. through Dec. 24. $18 to $32; discounts for children. Pay-what-you-will performance this Wednesday, call for details. (714) 708-5555. Running time: 2 hours.