The story begins from the context of a stranger born as Yankee. He starts by describing how practical his life has been. He talks about his skills in operating and fixing machines and then he talks about how one day his life took a rather interesting turn after he got in a fight and got knocked out by a hit with a crowbar on the side of his head. After he regained consciousness, a knight takes him as a prisoner to Camelot. Then he dozes off while the narrator begins to narrate the story from a manuscript.
The Yankee wakes up and finds a naked lady in front of him who is equally surprised at seeing him. He soon finds himself in a city full of peasants. Seeking answers, he interacts with an old man but finds nothing. Next, Clarence reveals the date to him which turns out to be 19th June, 528. The Yankee waits for further verification of this information by checking the eclipse that took place in 21st June, 528. However, before that date, he is taken to the hall of the Round Table where King Arthur, Merlin and the king’s knights, including Kay, reside where they decide on the when and how of the execution of the Yankee.
Clarence pays a short visit to the Yankee’s cell. There, he is informed about his death, which is scheduled to occur by burning. When the Yankee begs Clarence to help him escape, he is told that Merlin has cast a spell on him to prevent his escape from the cell. Noticing the fear of magicians in Clarence, he declares that he would blot the sun if they did not release him. The execution is moved up a day, which is the 21st of June, upon the declaration of his threats. The Yankee threatens to darken the sun and Arthur agrees to make him Chief Executive and Minister after the eclipse occurs as predicted by the Yankee.
Merlin soon challenges the Yankee about his claims of having magical abilities and he ends up back in prison for the act. The Yankee then pretends to burn down Merlin’s tower with lightning, which he actually manages to pull off successfully by using gunpowder and a rod at the top of the tower with a trigger. Soon after he claims to do so, he triggers the mechanism into exploding the tower. He gets a title equivalent to “The Boss” by the people.
The Yankee plans on gathering report for his future newspapers by employing a priest from the Dept. of Morals and Agriculture. During the joust among knights, he makes remarks about Sir Dinadan’s unhorsing but Sir Sagramor le Desirous mistakes it to be made about him. He challenges the Yankee to joust but instead of accepting the challenge, the Yankee asks for a four-year duration for the development plans of the kingdom that includes improvement in mining, school system and religion differentiation along with secretly planning to draw telephone and telegraph lines. The Church interferes in this case although the revenue is increased for the implementation of the plans.
The next challenge faced by the Yankee is the request of Alisande to save her mistress and 44 other princesses from three giants. All the knights volunteer but Arthur assigns the task to the Yankee. Soon, he is armoured and mounted on a horse to gather information about the castle. The armour discomforts him and they (the Yankee and Alisande) take shelter under a rock in the rain. The next day, they meet peasants on the road and have breakfast with them while discussing democracy. He scares seven knights by fooling them, using a blowpipe as a magical object.
The Yankee inquires after the captured knights and soon Alisande starts to narrate a monotonous tale. He meets Sir La Cote Male Taile who fails to sell soap to Le Fay’s castle. The Yankee visits the castle and there she tries to execute the lot but fails to fulfil her short-tempered commands of execution out of fear for the Yankee. He soon releases the tormented prisoners who had been imprisoned for silly reasons. The Yankee discovers that the knights were a duke and his sons who have been previously overcome by Sir Marhaus. The Yankee makes later plans to undermine the church by using the knights as advertisement billboards.
Next, all of them arrive the ogres’ castle to find the place to be a pigsty with three swineherds. The Yankee soon releases the hogs which Alisande treats as guests. The next scene showcases how the Church approved of slavery and how the Yankee inwardly despises the slavery procession. The Yankee is again called upon, this time to fix a dried up well. Merlin attempts to solve the problem but fails to fix it. After the Yankee arrives, he manages to fix the crack in the well with the usage of a pump, another magical device.
Meanwhile, the monks have been told that God desires them to use the well for shower. After the abbot starts, all the other monks follow. At the same time, King Arthur gains news of an imposter magician. He arrives and gets rid of the magician. Other events: the Yankee calls upon a priest from West Point to answer the examination board; he also discusses about making some changes to the military system. Afterwards, the Yankee mints some coins and finds that Clarence has released a newspaper.
King Arthur and the Yankee plan on putting on disguises by dressing up as peasants and roaming the countryside. The king takes some time in adjusting to the character. He refuses to bow down to the nobles and for this disobedience, he receives whips but fortunately, the Yankee takes them on Arthur’s behalf. Next, when Arthur compares the Yankee’s predictions to Merlin’s, the Yankee claims to know the future from thirteen and a half century later. Arthur begins to further quiz him but he gets chased by knights and in the end, he joins them after hearing the stories of the sufferings of the peasants by the Church.
The King and the Yankee leave the place after they notice a fire in a manor with a family hanged nearby. The cottagers tell them about how the poor family got hanged for murdering their lord via a mob. A charcoal burner named Marco is sent to provide justice for the remaining members who had escaped the slaughter but the Yankee dismisses him of the duty. They save some troubled children. Next, they have an extravagant meal at Marco’s and the King sleeps. When the King awakes from his sleep and begins to talk gibberish as a part of his role, the people consider killing the two guests and chase them into the woods. They are saved by noble men and are taken safely to an inn where they witness slavery up-close. They are taken as slaves for sale there. Upon failing to provide proof of being freemen, they are sold and experience the life of slaves. Finally, they are sold to a man whom they manage to trick and kill. Fortunately, they regain identity with Clarence’s help.
Four years after the joust duel, the Yankee is forced to finally accept the challenge ha had delayed for these few years. By then, the tournament had declared the usage of any weaponry legal. Merlin equipped Sir Sagramor with an invisible veil while the Yankee used a rope to lasso him and all the other knights present. After almost eight bouts, Sagramor challenges Yankee with his sword and the Yankee kills him with a revolver. Then, he challenges the rest of the knights to kill him to which they accept defeat and thus, knight-errantry is abolished.
After that day, the Yankee reveals to the world his projects: new industries, educational systems, newspapers and democratic practices. These projects start bringing forth gradual prosperity. He marries Alisande and they have a child named Hello Central who suffers from membranous croup. They go to France and upon returning, discover that Mordred and the Church has made plans to ruin his nineteenth-century civilization. Yankee plans on training his elite 52 disciples and use electric fences and land mines to kill the knights.
The last chapter draws the ending by explaining that just when the Yankee and Clarence approach the wounded for assistance, the Yankee is stabbed. Merlin, disguised as a woman, offers them treatment and food. Clarence finds that Merlin had cast a spell on the Yankee to sleep for the next thirteenth centuries. His manuscripts of industrialization are buried with him in a cave to secure his body. The narrator reveals that the manuscript ends here as dawn commences and all he sees is a stranger who calls out for Sandy and approaches the King to lower the drawbridge. Then he dies.