Mary Call Luther lives in the rural Appalachian mountains, and she and her family have been long beset by debt and poverty. Her father, Roy, has been sick for a long time, and Mary Call has been in charge of taking care of her siblings, a role which she has risen to mightily.
In the depths of his illness, Roy makes Mary promise that she will always keep their family together and under their roof. This process is aided when their landlord—in the depths of a sickness of his own, heavily disoriented by fever, and convinced of his coming death—insists on signing over the deed to their house so they can be free of their debt to him.
Still, their problems intensify when Roy finally dies of a sudden stroke. This puts the family's unity in enormous jeopardy because, without an adult caretaker, social services (to Roy, the "county people") will surely take the children and separate them into foster homes. Mary's promise to keep the family together looms over her, and her father reinforces the importance of his wishes by imploring her not to call a preacher or an undertaker after he passes in order to keep his death a secret. He asks instead to be wrapped in a sheet and buried under one of the mountains bordering the valley they live in, Old Joshua, and Mary sets hard at work to keep the secret safe.
This task isn't easy, but Mary is determined to do her very best for her siblings and her father's memory. She deftly navigates the social complexities of hiding her father's absence from their schoolteacher, neighbors, and the nosey (ex?) landlord, Kiser, while also struggling to teach herself the art of wildcrafting medicinal plants to sell to a local pharmacist in order to support herself and her siblings financially. There are certainly bumps in the road, but Mary is a wonderful caretaker.