From a distance, Andrew Wyeth's 1948 painting looks like a young girl daydreaming in a summer field. In reality the figure is Anna Christina Olson, a 55-year-old woman with a severe degenerative muscular disorder, dragging herself across her family's farm in Cushing, Maine. This episode tells her story. Born in 1893, she lived her entire life on that property, and by her late twenties could no longer stand or walk unassisted. She refused a wheelchair and chose instead to crawl, pulling herself through floorboards, mud, and grass on her own terms.

We look at Wyeth's nearly 30-year relationship with the Olson family, the moment he saw Anna from an upstairs window making her way up the incline toward the house, and the choices he made in the studio: egg tempera on a gessoed panel built up in tiny overlapping strokes, a torso modeled by his wif ...