In the book, a Yankee engineer from Connecticut is accidentally transported back in time to the court of King Arthur, where he fools the inhabitants of that time into thinking that he is a magician, and soon uses his knowledge of modern technology to become a “magician” in earnest, stunning the English of the Early Middle Ages with such feats as demolitions, fireworks, and the shoring up of a holy well. He attempts to modernize the past, but in the end he is unable to prevent the death of Arthur and an interdict against him by the Catholic Church of the time, which grows fearful of his power.
In addition, many passages are quoted directly from Sir Thomas Malory’s Le Morte d’Arthur, a medieval Arthurian collection of legends and one of the earlier sources. The narrator who finds the Yankee in the “modern times” of Twain’s nineteenth century is reading the book in the museum in which they both meet; later, characters in the story retell parts of it in Malory’s original language. A chapter on medieval hermits also draws from the work of William Edward Hartpole Lecky.
The story begins as a first-person narrative in Warwick Castle, where a man details his recollection of a tale told to him by an “interested stranger” who is personified as a knight through his simple language and familiarity with ancient armor.
After a brief tale of Sir Lancelot of Camelot and his role in slaying two giants from the third-person narrative—taken directly from Le Morte d’Arthur—the man named Hank Morgan enters and, after being given whiskey by the narrator, he is persuaded to reveal more of his story. Described through first-person narrative as a man familiar with the firearms and machinery trade, Hank is a man who had reached the level of superintendent due to his proficiency in firearms manufacturing, with two thousand subordinates. He describes the beginning of his tale by illustrating details of a disagreement with his subordinates, during which he sustained a head injury from a “crusher” to the head caused by a man named “Hercules” using a crowbar. After passing out from the blow, Hank describes waking up underneath an oak tree in a rural area of Camelot, where he soon encounters the knight Sir Kay, riding by. Kay challenges him to a joust, which is quickly lost by the unweaponed, unarmored Hank as he scuttles up a tree. Kay captures Hank and leads him towards Camelot castle. Upon recognizing that he has time-traveled to the sixth century, Hank realizes that he is the de facto smartest person on Earth, and with his knowledge he should soon be running things…