The preface is a disclaimer signed by Twain, stating that while he does not know for sure sixth-century England had all the particular faults he ascribes to it in the book, he knows they existed later in England and other civilized countries, and the sixth century probably had worse vices to fill the place of any of these that were lacking. He says the question of the divine right of kings is not settled in the book and that, for convenience, he took the view that it does not exist, but he will put his mind to it and try to give a definite answer sometime next winter. In the Explanation, the narrator meets a stranger on a tour through Warwick Castle who talks familiarly of medieval times and the court of King Arthur. They come to a suit of armor that belonged to Sir Sagramor le Desirous with a bullet hole in it, and the stranger claims to have put the bullet there himself. The stranger leaves, and the narrator goes back to his room and reads from Malory's Le Morte d'Arthur. The stranger appears at his door, and the narrator brings him in and makes him welcome.
The stranger begins to tell his tale, how he was born a Yankee in Connecticut and grew up practical and skilled with machinery, and how one day he got into a fight and was knocked alongside the head with a crowbar. He wakes up and is taken prisoner by a knight in armor, who takes him to Camelot. He assumes the knight is either a circus-performer or crazy and that Camelot must be the name of an asylum. Stranger begins to doze off, so he brings the narrator back to his room and gives him a manuscript that tells his story. The rest of the book is taken from the manuscript.
Twain's anti-monarchical sentiments already show through in the preface, as do some of the book's chronological curiosities. The narrator describes the stranger's smile as belonging to another time, and his speech patterns are likewise archaic. The Yankee seems to belong entirely to the sixth century during his appearance in the frame story, which seems to imply that he undergoes the reverse of the process experienced by Clarence, who developed from a sixth-century man into a nineteenth-century one.
The selection from Malory's Le Morte D'Arthur, which the narrator reads before the stranger's appearance at his door, is appropriate, as it provides background information for an episode that will occur shortly into the Yankee's narrative. This and the other excerpts from Malory scattered throughout the book acknowledge Twain's debt to the earlier author and provide a firm grounding in Arthurian tradition. The fact that the manuscript is a palimpsest, written over some old monkish legends, gives credence to the stranger's claims of its age, but it raises the question of why the Yankee didn't have clean paper from his factories.