Percival takes over the family business when his father dies, which means that he and Nellie will remain in New York permanently. Distraught by the news, Harriet falls into a depression.
Nels and Harriet's newly adopted daughter Nancy seems to be the reincarnation of Nellie - except for one thing: Nancy is worse than Nellie.
The Ingalls' growing household is a little crowded for James, who feels hurt by Albert's rejection.
When Doc Baker's workload becomes too much for one person, he requests a new graduate to help him. He gets more than he expected when the new arrival turns out to be black.
Harriet is pressed to transform the Walnut Grove restaurant into a chain called "Mrs. Sullivan's." Meanwhile, Charles is left to gather the slack at home with Caroline so in-demand as one of the cooks.
Mary, Adam, Hester Sue, and the Wilders all make a special visit to Charles and Caroline's for Christmas Eve. An unrelenting blizzard prevents everyone from heading home after dinner, but they all pass time by recalling Christmases of personal significance in their lives.
A young boy with a stuttering problem is befriended by James.
Charles and Almanzo jump at an opportunity to make money taking a delivery to Arizona, although it means being away from home for an extended time. Meanwhile, a pregnant Laura struggles to keep her newly planted orchard alive during a severe drought.
After an acquaintance dies suddenly, Charles is prompted to give up farming in favor of building a legacy on his hand-crafted furniture.
James and Cassandra's uncle, who wanted nothing to do with the children following their parents' deaths, arrives unexpectedly in Walnut Grove and takes an interest in them. But it turns out he's interested in custody of them as well.
Sam Terhune arrives in Walnut Grove looking for work, and finds favor with all of the townsfolk - except for his ex-wife, Hester Sue.
The Wilders' marriage is put to a severe test when Almanzo, who is recovering from diphtheria, does not take proper care of himself and ends up having a severe stroke. The friction between husband and wife is aggravated by an unexpected visit from Eliza Jane.
Laura's anticipation of the birth of her first child is tainted by Almanzo's increasingly bitter attitude towards his debilitating health, as well as the possibility that they might lose their home. Eliza Jane's solution to their problems complicates everything.
Mr. Edwards has returned to alcohol to soothe the pain of his deceased son, and his wife takes the other children and leaves him. Laura wants Mr. Edwards to be godfather to her baby, but the alcoholism threatens to ruin this as well.
Caroline receives a letter from an old friend, living in a miner's camp where there's been an outbreak of influenza, who is summoning her for help.