A local mill operator undercuts Hanson's Mill when he sells his stock of cornmeal to the residents of Hero Township at less than half of what Hanson is asking.
The people bite, but it's not long before they are stricken with the "Plague."
Mr. Peterson is a newcomer to Walnut Grove but is having trouble competing with both the Mercantile and when he comes across a stock of cornmeal from a dealer (unseen), he is able to buy it at a low price, and then – knowing that many of the locals are having trouble making ends meet and need cheap food – he sells it at a bargain price.
Unknown to perhaps even Peterson, the cornmeal has been infected, and the terrifying signs are seen when a little rat peers from behind a stack of the sacks, crawling onto one of the bags and trying to claw its way in.
Two supper scenes are seen. First, the Boulton family, one of those families dealing with hard times, sits down to supper. They are elated that the kindly Peterson was able to provide them the gift of food at a reasonable price ... so reasonable they now have enough of a food source to last several months, much more than if they had gone to the reliable Hansen. As they are eating their cornbread and otherwise eating well, cut to a scene of fleas on top of the opened sack of cornmeal.
Then, the Ingalls family, where Charles' involvement in the storyline is set into motion when Laura complains about her inability to chew meat (presumably because of a loose tooth). While at Dr. Baker's office, everyone is engaged in their usual light-hearted banter when Mr. Boulton bursts in, literally breaking the door down. His son is burning up with fever and his wife is half-conscious, doubled over in extreme pain. Charles sends Laura home as he and Dr. Baker make a mad dash to the Mercantile for ice and some rags.
The church is turned into a makeshift hospital as Dr. Baker and Rev. Alden become the main doctors in town, treating increasingly more and more people for what is suspected to be typhus. Charles later spots a runaway wagon with no driver ... and later finds his neighbor friends, the Harpers, collapsed and half-conscious and also with symptoms of typhus. Exposed to the illness, Charles briefly stops by home to tell Caroline and his daughters he'll be away for some time and not to come to visit for any reason. Several people die, and others are no longer afraid of death because death will be better than enduring typhus.
As the number of cases increases and Dr. Baker is at a loss for an explanation, Mr. Edwards – one of the folks who bought the cornmeal when he was running short of funds – lets slip that he bought the cornmeal and that he was eating it like a famished hound. Charles instantly realizes that the cornmeal must be infected and he and Dr. Baker make a mad dash to Peterson's shop.
No answer at the door.
They break in and find Peterson, deliriously ill. Charles tries demanding answers but when he mumbles incoherently (turns out he himself has fallen ill), they demand the keys.
Which they get.
And they also get a frightening surprise when they open the warehouse door:
RATS!
Dozens of them, crawling around the storeroom, getting into the sacks, eating the cornmeal and leaving their fleas behind.
"All this time, it's 100 yards away!" an outraged Dr. Baker realizes, before ordering, "Burn this place to the ground!"
After taking Peterson to safety (and presumably removing the cash he had made), cut to a shot of the warehouse and office engulfed in flames. Charles, Rev. Alden and Dr. Baker are watching as each are holding kerosene cans. (Presumably, they had soaked the boards with kerosene then set a fuse to instantly send the shed up in flames, before the rats – if they even knew what hit them – have a chance to escape.)
News (presumably) quickly spreads about the infected cornmeal and that anyone who bought it should destroy it immediately. Meanwhile, the people who had fallen ill soon recover from their illnesses and about two weeks later, the final patients have recovered and are able to go home. Dr. Baker reveals he's going home to sleep for about two weeks, while Rev. Alden gives thanks that the crisis has passed and Mr. Edwards is invited to supper at the Ingalls'.
Tropes associated with this episode:
- Anyone Can Die: While none of the major characters do, the typhus outbreak – although localized – proves that no one is immune to death.
- Burn Baby Burn: Dr. Baker orders Charles to burn the warehouse (where the infected cornmeal is kept) to the ground. ("Burn this place to the ground") And they and Rev. Alden do, immediately upon soaking the boards with kerosene and – after rescuing the manager (who is delirious after having fallen ill, and having had rats crawl all over him) – setting it on fire. The rats are presumably burned to death as the source of the plague is contained and eliminated.
- Dr. Baker, burning his clothes inside the church to get rid of any trace of the typhus.
- Death of a Child: Mr. Boulton's son perishes from the Typhus.
- Despair Event Horizon: Charles goes to the Bolton place, where the wife was already dead to see how the son is going... and finds the Bolton patriarch, holding the body of his son, and saying it's "too nice a day to go to school".
- Irony: A farming family is thankful for the kind mill owner who sold them cornmeal ... unaware that it will lead to the mother dying and both the father and his son becoming deathly ill.
- Man Bites Man: The drama of the episode is balanced with a light-hearted moment where, at the Ingalls' supper table, Mary and Laura recount how they got into a scuffle with Willie Oleson, who bit Mary one day at recess. Caroline doesn't usually condone violence ... but this one time, she admits she wouldn't mind if Mary "cuffs him something fierce".
- Nightmare Fuel: In-universe; even with their suspicions confirmed, Charles and Dr. Baker seem horrified when they open the storeroom and find dozens of rats swarming around the sacks of cornmeal.
- The Plague: Exactly What It Says on the Tin – a typhus outbreak, caused by people eating cornmeal infected by the rats.
- Right Under Their Noses: "All this time, it's 100 yards away!" declares Dr. Baker when he and Charles see the rats swarming through the cornmeal.
- Sleep Deprivation: Dr. Baker gets very little sleep for about a week, literally the only doctor – with makeshift help from Charles and Rev. Alden – who can care for a growing number of sickened people.
- Swarm of Rats: As the drama intensifies throughout the episode, more and more begin appearing in the warehouse where the infected cornmeal is kept. By the time Charles and another farmer determine the source and open the warehouse doors, the place is literally crawling with hundreds of rats, getting into the sacks and eating the cornmeal.
- Terrifying Pet Store Rat: The rats that swarm the stored cornmeal are not wild rats. The shiny coat each rat has clearly shows that these are domesticated pet rats. Even the first rat shown in the first minute is a domesticated rat.
- The Tooth Hurts: During the scene at the Ingalls' supper table, Laura complains that her tooth hurts when she's eating some baked steak and can't put any pressure on it. Charles taking her to see Dr. Baker indirectly sets about the main plot.
- Wham Line: Dr. Baker has them both: "All this time, it's 100 yards away!" and "Burn this place to the ground!"
- What Happened to the Mouse?: No pun intended, as it is presumed the rats never really knew what hit them. As for Mr. Peterson (the salesman who sold the cornmeal at a deeply-discounted price), it is not revealed in the postlogue, nor is it ever stated if he faced any consequences, or even if he knew what he was selling, much less his fate. The fates of several of the patients are never really stated either; the only confirmed deaths are Mr. Boulton's son and wife.
