It is night. A lone black woman walks through a cornfield in South Carolina. The stars wink above her. Crickets and cicadas grow quiet as she passes and then resume their orchestral humming, now punctuated by the sound of rustling leaves a little farther off. She moves toward an unpainted one-room building. When she gets there, she will have to rely on oil lamps for light. A group of African American adults will be waiting, eager to learn what she has come to teach them. It could be 1863 or 1916 or 1935. She could...