“Getting back on the horse” is a cliche that should be retired, so basing an entire play around the concept might not be the best idea. But Sarah Ruhl’s Late: A Cowboy Song thankfully doesn’t dwell on cowpokes and saddles, even if it does begin with a woman learning to ride a horse. The play revolves around Mary, a wife and new mother; her husband, Crick; and Red, an enigmatic cowgirl Mary meets on the outskirts of Pittsburgh. Through the course of the play, the characters explore gender roles, poverty, and the nature of love, while Red sings a series of folk songs that explain the plot. It’s certainly less zany than No Rules’ rather madcap last season, but the somber undertones will stick with audiences long after the last cowboy songs fade out. The show runs Jan. 1 to 19 at Signature Theatre, 4200 Campbell Ave., Arlington. $15. (571) 527-2159. norulestheatre.org.