Magic and Mirth : ‘La Posada Magica’ takes a lively journey through the heart.

One baby has died. Another is about to be born.

Not just the customary Christmas fare. But “La Posada Magica� at South Coast Repertory, now in its fourth year, has become the Southland theater scene’s most vital and most locally flavored holiday tradition.

Octavio Solis, directing his own play, uses the posada, a custom in which members of Latino communities go door to door, reenacting the journey of Mary and Joseph as they searched for shelter. Neighbors are supposed to respond with good cheer and charitable gifts.

Gracie (Crissy Guerrero), a ninth-grader whose baby brother has just died, doesn’t feel charitable. When the posada comes calling, she’s more in the mood to sabotage their effort than to help. She throws the procession into chaos, but then . . . yes, there is a happy ending.

Despite the subject, Solis’ work has moments of hearty comedy, thanks to some of the characters in the posada such as the hip Refugio (Thom Rivera) and a couple of chocoholics (Denise Blasor, Christine Avila). Marcos Loya’s score, performed live, enriches the story immensely, as does Cliff Faulkner’s sparkling ornament of a set.

* “La Posada Magica,� South Coast Repertory Second Stage, 655 Town Center Drive, Costa Mesa. Tuesdays-Fridays and Dec. 22, 8 p.m.; Saturdays, 3 and 8 p.m.; Sundays and Dec. 24, 12:30 and 4:30 p.m. Ends Dec. 24. $10-$25. (714) 708-5555. Running time: 2 hours, 10 minutes.