Laura and Mary get into a petty tiff about a boy who fancies the latter more and sees Laura as a kid. Laura regrets this when her sister starts struggling to see, even with glasses, and knocks a lantern over and starts a fire. An examination indicates the worst outcome is nigh: her parents learn that the nerves of her eyes are weakening and deteriorating with each passing day, and it's going to progress without any hope of stopping... soon, she will go blind.
To Mary's horror, her eyesight starts to fade very quickly, into total blindness. One awful morning, she awakes to the sight of absolute darkness and wails in terror. Afterward, she spends a long time confined to a chair and endlessly bitter at being robbed of everything that mattered to her and turning into a burden. With her dreams shattered, Mary becomes despondent, until she's made to go to a place that can give her hope back by teaching her how to live with her handicap, where she meets Adam Kendall, a blind teacher who understands her pain and knows exactly what Mary needs to bounce back. Mary is given a chance to start life again, and grow close to someone who is so fond of her that a romance eventually blossoms.
However, Walnut Grove is not so lucky, because a bad year for crops where the bottom fell out has brought the community to near bankruptcy, and its inhabitants are faced with the need to move elsewhere to make ends meet.
Tropes associated in this episode:
- Based on a True Story: Mary going blind due to scarlet fever and being sent to a blind school in Iowa to help her cope with her new circumstances are taken from the books.
- Broken Tears: By Charles and Caroline as Mary screams out in horror that "I CAN'T SEE!!!!!" ... and know there's nothing they can do.
- Last Episode, New Character: Averted due to the series being renewed in the summer of 1978. However, as this was thought at one point to be the last episode of the series, Adam Kendall is introduced as Mary's teacher and confidant. As the series was renewed, he'd become her husband.
- Manly Tears: Charles has cried in a number of episodes before this, but upon hearing Mary screaming in horror that she is completely blind sends him over the edge emotionally unlike any episode beforehand or since. Days before she actually loses her sight, Charles trembles with emotion as he tries to tell Mary that the scarlet fever will worsen her already failing eyesight.
- Put on a Bus: Walnut Grove schoolteacher Mrs. Simms (formerly Miss Beadle) makes her final series appearance.
- Series Fauxnale: Some histories claim that this episode was to be the final episode, with the Ingalls deciding to move from an economically troubled Walnut Grove (which serves as the subplot for the main story, which is Mary losing her eyesight). In fact, the entire citizenship of the financially crippled town of Walnut Grove gather at the church one last time to say goodbye. However, NBC ultimately decided that, given Little House was a rare hit on its primetime schedule – and they really couldn't put all their faith in shows like Supertrain or Cliffhangers (both then under development) – the series should return for a fifth season … and it would.
- Wham Line: "I CAN'T SEE, PA!!!! I CAN'T SEE!!!!!!!" Mary's horrifying realization when she realizes that, in her sleep, she has lost the last of her failing eyesight. With highly dramatic music added and Charles and Caroline's emotional reactions,
often panned as highly melodramatic.
