A Connecticut Yankee in King Arthur's Court is a "framed story." That is, the first chapter tells how a tourist in England, presumably Mark Twain, meets a stranger who tells him part of his story and then gives him a manuscript that tells the rest of his strange tale. In the last chapter, the tourist has finished reading the manuscript and searches out the stranger, only to find him dying and calling out for the wife and daughter whom he had lived with in sixth-century England.
In the first chapter, this stranger (we later learn that his name is Hank Morgan, but he is usually referred to in the novel as The Boss) tells the tourist that he was something of a jack-of-all-trades who had a particular aptitude for making and inventing things mechanical. He is from Hartford, Connecticut, where he had been head superintendent in a munitions factory until, in a fight with one of the workers, he was hit in the head with a crowbar. When he awakened, he was sitting in the grass under a tree. A man in old-fashioned armor took him prisoner, and they rode off to what Hank Morgan believed would probably be an insane asylum. At this point in the story, this stranger begins to feel very sleepy, so he gives the tourist the manuscript detailing his adventures, which he has written from the journals that he kept.
The first chapter of the manuscript (the introductory chapter is technically a prologue) begins with the knight and Hank Morgan riding through a quiet countryside that Morgan does not recognize. After a time, they arrive in a small, wretched town and pass through the gates of a huge castle; they then enter into a great paved court.
Trying to find out what asylum this is, Hank Morgan talks with a young man who tells him that the year is 528 and that the day is June 19; Morgan has been captured by Sir Kay the Seneschal, and he will be exhibited before the court. Then he will be sent to the dungeons to either rot or be ransomed.
At the feast around the Round Table, Sir Kay's turn to tell of his adventures finally arrives, but he is interrupted by Merlin, who tells the story of how King Arthur got his sword from the Lady of the Lake; he puts the entire crowd to sleep. When Sir Kay does tell his story, he exaggerates immensely. Then Arthur sentences Morgan to die at noon on the 21st. Morgan is stripped of his "enchanted" clothes and is hauled off to the dungeons.
When Clarence (the boy to whom he had talked) comes to visit him, Morgan tells the boy to take a message to the court; he says that he is a magician more powerful than Merlin. The message has some effect, but Merlin ultimately scoffs at the claims of this "magician" because the so-called spell that Morgan says that he will cast is not specified. By this time, Morgan has remembered that there will be an eclipse of the sun at noon on the 21st, so Morgan sends Clarence back to tell the court that he will blot out the sun—if he must.
Shortly thereafter, Morgan is hauled out to the courtyard and chained to a stake. A monk is praying for him when, suddenly, he stops, and Morgan notices that the solar eclipse is just beginning. He realizes that when he asked Clarence what day it was, Clarence gave him the incorrect day. Thus Morgan puts his knowledge of the eclipse to good use, thereby gaining his freedom and a position as "perpetual minister and executive" to the king, as well as liberal funding, if he will "let" the sun shine again. He keeps the king and the knights in suspense for a time, ostensibly to make sure that the king meant what he said; then, when he notices that the eclipse is total, he announces that his spell will now begin to pass away.
This "miracle" makes Morgan a man of great interest to the people of the kingdom, and when Merlin begins spreading rumors about him, Morgan blows up Merlin's tower, using explosives which he and Clarence have made. This "miracle" solidifies Morgan's position in the country.
At one of the frequent tournaments held in Camelot, Sir Dinadan (who tells many bad jokes) is being drubbed by Sir Gareth, and The Boss (as Morgan is now called) says that he hopes that he (Sir Dinadan) dies. By the time these ambiguous words are uttered, however, Sir Gareth has crashed into Sir Sagramor le Desirous, and Sir Sagramor thinks that Morgan's derogatory wish was meant for him. Sagramor therefore challenges Morgan, The Boss, to a bout after he, Sagramor, returns from questing after the Holy Grail. The king and others urge The Boss to also undertake a quest so that he will be more worthy of taking on Sir Sagramor. Morgan puts off this journey for some time, though, so that he can make some changes in the kingdom—such changes as providing some schools, factories, military academies, telephones, and telegraph lines; all these changes are done quietly, of course, so that they will not be too noticeable immediately.
Finally, Morgan can put off his quest no longer. The king decides that Morgan will accompany the Demoiselle Alisande la Carteloise to free her mistress and forty-four princesses held captive by three giants with one eye each.
Along the way, Morgan, The Boss, discovers many things; first, he learns that armor is very uncomfortable to ride in and also to sleep in. Then he and the Demoiselle have a meal with several freemen, one of whom is willing to think about change; as a result, he is sent back to Camelot for Clarence to put into training. A little later, The Boss terrifies six armed knights by stoking up a head of smoke with his pipe as they charge at him; the knights halt, amazed, and are willing to surrender. That evening, the evening of the second day out from Camelot, they come upon the castle ruled by Morgan le Fay. Although the wicked le Fay has a quick temper and is willing to kill anyone who crosses her even slightly, she becomes very deferential when she learns that her visitor is The Boss. She allows him his way even after he frees a man accused of killing a deer on the royal preserve and even though he frees nearly all of the prisoners in her dungeons. She casually stabs for a young boy, but she refrains from throwing his grandmother, who curses her for that deed, into the dungeons.
Several days later, Sandy (the name which Morgan has given his traveling companion) informs The Boss that they are coming upon an ogres' castle. The Boss, however, can see only a pigsty filled with pigs, but Sandy assures him that it is a castle and that those are princesses (and not pigs) who must be freed. Rather than argue with her, The Boss agrees that this castle must surely be enchanted—but enchanted for his eyes only. Thus, he rides down and buys the pigs from the swineherds. He and Sandy then drive the pigs to a nearby castle, where the "princesses" will wait to be reclaimed by their kin or friends.
When The Boss and Sandy meet a band of pilgrims heading toward the Valley of Holiness, they also decide to travel in that direction. On the way, they meet one of The Boss's "sign board knights," knights who are advertising various products which The Boss wants to introduce into England. But it is not long before they learn that there is a problem in the Valley of Holiness that requires one of the Boss's spells to set right, so he sends a knight back to Camelot with a note to Clarence for supplies and helpers.
The problem in the Valley of Holiness is that the holy well, believed to be the product of a miracle in an earlier day, has gone dry. The Boss examines it and finds that a section of the wall has been broken. While he waits for his supplies and aides to arrive from Camelot, he insists that professional courtesy requires him to wait until Merlin gives up before he takes over. Merlin does finally admit that he has failed to fill the well, but he gives up just as two of The Boss's helpers arrive; when they do, they quickly repair the hole in the well's wall, and then they prepare to make a spectacle of the restoration of water to the well. The "miracle," of course, is a success, and The Boss's reputation is reaffirmed.
A short time later, however, another magician arrives, and for the moment, he eclipses The Boss's reputation. All is not lost, however. Using a telephone that has just been installed in one of the abandoned caves in the Valley, The Boss predicts that the king and his retinue will be in the Valley of Holiness in two days; the other magician insists that the king will be traveling in the other direction. When the king does arrive on time, the other magician is discredited.
While the king is there, he dispenses justice, he oversees the choosing of officers for the standing army (a process that The Boss is unhappy with), and he allows those who are ill to attempt to heal themselves by touching him. After this business is taken care of, The Boss and the king set out to travel into the countryside in disguise. The Boss wants to find out, firsthand, what the conditions of the country are, and the king thinks that it might be a lark to go along. Thus, the two set out.
