Sierra Repertory Theatre’s The Robber Bridegroom, a “country and southern” comedy, steals its way on to the Fallon House stage Friday, Sept. 2 through Sunday, Sept. 25. Inspired by the Grimm fairy tale of the same name and based on Eudora Welty’s 1942 novella, the musical takes place in late 18th-century America. As the show opens, the cast appears and sings of their ancestors along the Natchez Trace, Mississippi, and the story that’s about to unfold.