Set in 17th century Puritan Boston, Hester Prynne gives birth to an illegitimate child and is condemned to wear the scarlet letter 'A' as a sign of her adultery. Hester refuses to reveal the identity of her lover, and is forced to lead a life of humiliation. Meanwhile, Hester's husband settles in Boston and after making her swear to keep his identity secret, tries to discover who Hester's secret lover is.

《紅字》是以兩百多年前的清教時代背景寫成的愛情故事，女主角所犯的通姦罪在當時社會的道德標準下是十惡不赦、罪無可恕的，反映了當時人們深受宗教規條的約束。女主角雖受到無情的揶揄和排斥，但她仍能堅強面對逆境，把女兒撫育成人，她既堅強又慈愛的形象深入民心。