In writing Main Street, Sinclair Lewis paid little attention to formal plot development. Consequently the narrative presents a series of episodes rather than a tightly constructed plot.
Carol Milford Kennicott, a graduate of "sanctimonious" Blodgett College, with a year of additional study in a Chicago library school, works as a librarian in St. Paul (Minnesota) for three years before her marriage to Dr. Will Kennicott, of Gopher Prairie. She is a rebel against ugliness and conformity, and one factor in her decision to accept Kennicott is the opportunity to make over a planless middle west prairie town.
The story proper begins when, after a honeymoon in the Colorado mountains, the Kennicotts approach Gopher Prairie on the train. In the drab town are three thousand dull people, in a social strata ranging from Swede farmer to bank president. Main Street has two-story brick shops flanked by Fords and lumber wagons. There is no park to rest the eyes. The Kennicott family home is outdated and stuffy. The prairie, vast and empty, stretches away on every side.
Dreams end and realism begins when Carol takes a thirty-minute walk, inspecting the town, north and south, east and west. It is then that she realizes the shabbiness surrounding her. Her first social evening is also a disappointment, for she finds the conversation of both men and women personal and trivial. She tries to introduce something different. On the way home, however, she is lectured by her husband on the danger of shocking people.
As time goes on, Carol makes one attempt after another to enlist the help of others in uplifting Gopher Prairie. An early project is the formation of a dramatic club, which functions just long enough to present one mediocre production, The Girl from Kankakee. Carol becomes a member of the Jolly Seventeen, a bridge club composed of an elite group of young married women. She also joins the Thanatopsis Club, a literary organization, and tries to change the club programs, which are stilted and superficial. Her suggestions make little headway. Her appointment to the library board gives her a chance to express her opinions about books and reading, but her ideas are not welcomed by the local librarian, whose policy is to keep books clean by discouraging readers.
After the Kennicotts' child, Hugh, is born, Carol feels that her motherhood hems her in more than ever. The Smails, relatives of Dr. Kennicott, come to live in Gopher Prairie and are a constant irritant because of their critical attitude toward Carol and their interference with her household affairs.
Parallel with the story of the Kennicotts is that of Bea Sorenson, who becomes the wife of Miles Bjornstam, a free-thinking Swede. Their wedded life ends in tragedy, for Bea and her child, Olaf, both die of a fever. The townspeople blame Miles for their deaths. Still cynical, he leaves Gopher Prairie for Canada.
Carol's closest woman friend is Vida Sherwin, a high-school teacher, who later marries Raymond Wutherspoon. Vida is as domestic and conservative as Carol is nonconformist. Raymond, largely because of Vida's influence, blossoms out after marriage. He returns from the army to become manager of the Bon Ton, the highest-class store in town.
Carol is attracted to Guy Pollock, a lawyer who has ideas similar to hers, though he has waited so long to express them that he is now a victim of "Village Virus." Fearing that the same fate may be hers, Carol attempts one improvement project after another, all of them ending in failure. Percy Bresnahan, Gopher Prairie's multimillionaire native son, comes home for a visit and makes advances to Carol. She repels him with disgust.
The only serious extra-marital love affair in Main Street is that between Carol and Erik Valborg, a tailor's assistant five years younger than she. Dr. Kennicott puts a stop to the romance and makes plain to his wife the kind of life she would lead if married to the son of a Swedish farmer. Erik abruptly leaves Gopher Prairie on the Minneapolis train.
Still another episode is that introducing Fern Mullins, a young high-school teacher, who becomes involved with a pupil, Cy Bogart, at a barn dance. She is the center of a storm of disapproval and intolerance. Like Bjornstam and Valborg before her, Fern leaves town on the train. Finally Carol takes the train herself. She leaves Kennicott and spends almost two years working in Washington during World War I. She enjoys the cultural opportunities of the city but is willing after a time to return to her husband and Gopher Prairie. Their second child, a daughter, is born. Carol realizes that she has raged at individuals when institutions are really to blame and that although she is beaten, she has kept the faith. She predicts changes yet undreamed of if the baby lives out a normal lifetime. Dr. Kennicott's final remarks reveal that he is more concerned about the immediate present than the remote future. The reader realizes that the gap between wife and husband is still wide and that the novel really ends in an impasse.