I'll Be Waving as You Drive Away (Part 1)

What happens

Mary has fallen for a young man named Seth Barton, and life seems full of promise. But her eyesight, always weak, begins failing fast.

The doctor delivers devastating news: the scarlet fever Mary had as a child damaged her optic nerves, and she is going blind. As darkness closes in, Mary is angry and lost, and Charles has to help his daughter face a future she never imagined. One of the most famous episodes in the series.