Mary Ingalls begins to study for the state teachers exam she will take after she graduates from the Walnut Grove school. She falls in love with the new boy in town, Seth Barton. Mary begins to have tiredness in her eyes. Charles takes her to visit her eye doctor. At first, it's just eye strain, but her vision gets worse. She goes back to the eye doctor. After another exam, Dr. Burke tells a devastated Charles that Mary is going blind. Charles is in denial and can't bring himself to tell Mary. After Mary accidentally drops a lamp and says it seems dark in the room, Charles realizes he needs to tell Mary she's losing her eye sight. Charles finally tells a devastated Mary. Mary wakes up blind and scared. Dr. Baker suggests sending Mary to a school for the blind. Mary begs her parents not to send her. By the end of the episode, Mary leaves to go to the school.
