Carol Milford is a liberal, free-spirited young woman, reared in Saint Paul, Minnesota, the state capital. She marries Will Kennicott, a doctor, who is a small-town boy at heart.
When they marry, Will convinces her to live in his home-town of Gopher Prairie, Minnesota (a town modeled on Sauk Centre, Minnesota, the author's birthplace). Carol is appalled at the backwardness of Gopher Prairie. But her disdain for the town's physical ugliness and smug conservatism compels her to reform it.
She speaks with its members about progressive changes, joins women's clubs, distributes literature, and holds parties to liven up Gopher Prairie's inhabitants. Despite her friendly but ineffective efforts, she is constantly derided by the leading cliques.
She finds comfort and companionship outside her social class. These companions are taken from her one by one.
In her unhappiness, Carol leaves her husband and moves for a time to Washington, D.C., but she eventually returns. Nevertheless, Carol does not feel defeated:
I do not admit that Main Street is as beautiful as it should be! I do not admit that Gopher Prairie is greater or more generous than Europe! I do not admit that dish-washing is enough to satisfy all women! I may not have fought the good fight, but I have kept the faith. (Chapter 39)

Question: What is appalling to Carol about that place?
Answer: Its Backwardness
Alternative answer: That the town is ugly and conservative.