Mary falls in love with Seth. When Mary's eyesight starts to get worse, Charles takes her to a specialist. He is devastated when the specialist tells him that Mary will lose her sight. Charles is unable to tell Mary for a while that she is going blind. When Mary does go blind, the whole family suffers.
Elenco: Melissa Gilbert , Michael Landon , Lindsay Greenbush , Sidney Greenbush , Melissa Sue Anderson , Richard Bull , Jonathan Gilbert , Kevin Hagen , Matthew Laborteaux , Dean Butler , Dabbs Greer , Karen Grassle , Katherine MacGregor , Ruth Foster .