The story chronicles the rise and fall of the romance between Bartley Hubbard and Marcia Gaylord, who migrate from Equity, Maine, to Boston, Massachusetts, following their marriage.

Marcia Hubbard, lost and desolate in the gloom of her husband's abandonment, is a figure of fascination to Bartley's one-time friend Ben Halleck, who secretly is attracted to her.

He is torn apart by the situation of being attracted to a married woman, and bends over backwards to try and effectuate a reunion between Marcia and his former friend Bartley for whom he no longer has any feeling but contempt.

Even after the eventual death out West of Bartley, Ben Halleck continues to torment himself over what had been his transgressive love, unable to determine whether or not he should seize the chance and propose to her.

A Modern Instance is regarded as one of the most pivotal works in the career of William Dean Howells; it solidified his reputation as a champion of realism in the United States.