In 1933 in the Shenandoah Valley, there isn't a place for Lum (short for Columbia), a 33-year-old intersex woman. She travels by schedule from one branch of the family to another, assisting with cooking, childcare, and housework. Always an outsider, even in her own family, Lum secretly collects postcards of people like the Dog-faced Girl, imagining their stories, and nurtures her lifelong friendship with Smiley, an African-American man who sells furniture, odds and ends, and a little moonshine. She makes friends with another outsider, a young Melungeon man from an isolated community high in the mountains, who is fresh out of prison.

Scenes from Lum's childhood and young adulthood are interspersed with chapters taking place in 1933, when Lum is 33 years old. But Lum's world changes when a local banker becomes ill and needs care. Sent to assist, she forms an unlikely friendship with the curmudgeonly old man. At the same time, the federal highway administration comes scouting land, wanting to buy the family farm for a new scenic highway. Lum's relatives don't want to sell, and they're not alone. As tensions over the highway escalate toward violence, and as loyalties are tested, Lum takes a bold step to create an independent life.