A nineteenth-century engineer finds himself transported to sixth-century England, where he attempts to modernize the medieval world using his technological knowledge. Hank Morgan, a pragmatic factory superintendent from Connecticut, wakes up in the year 528 after a blow to the head. He must navigate the rigid social hierarchies of Camelot while contending with the influence of Merlin and the established nobility. Using his superior understanding of mechanics and science, he attempts to introduce democratic ideals and industrial progress to a society governed by superstition. The narrative is presented as a first-person account, blending humorous observation with an increasingly grim critique of power and human nature.

Readers frequently highlight the sharp contrast between the book's initial comedic tone and its eventual descent into violence and cynicism. Discussion often centers on Twain's use of the time-travel trope to expose the flaws of both medieval feudalism and the industrial age. Critics often note that the protagonist's attempt to impose progress on an unwilling society serves as a complex reflection of the author's own disillusionment. The work remains a subject of debate regarding its stance on technology, religion, and the nature of human progress. Many readers find the inclusion of the original illustrations essential for understanding the author's intended visual humor and social commentary.