Mama says we must be ready, ready for that angel coming. High in the hills of Kentucky, a little girl eagerly awaits the arrival of a very special visitor -- an "angel" who, she is told, will come riding up the mountain on horseback, carrying a baby sister or brother in her saddlebag. Li'l sis is what I'm wanting. Li'l sis is what I'll call her. I'll braid her hair right pretty, brush it out most every night. But the "angel" is not exactly what the young narrator imagined, and neither is the precious bundle that comes when she least expects it. This gem of a story highlights a little-known piece of American history: the Frontier Nursing Service, a pioneering group of women who came to be called "angels on horseback."