Okay, folks, get ready for a whole lot of names that have not been in use for hundreds of years, and a whole lot of swordplay. Here we go!
To start us off, King Uther of England falls in love with Igrayne, the wife of one of his vassals. With the help of the wizard Merlin, he disguises himself as her husband and sleeps with her, conceiving a son, Arthur. Arthur is hidden away with another of Arthur's vassals, Sir Ector, until one New Year's Day some time after Uther's death.
Then, Arthur manages to pull a sword from a stone (yep, that sword in the stone!) bearing an inscription that declares that anyone who can get that sword out becomes the King of England. Here's your king, England, whether you like it or not. Some grumbling of powerful barons and lords ensues, but by Pentecost, Arthur has been installed as the king.
Arthur's reign begins in turmoil as an alliance of twelve northern kings, led by Arthur's uncle King Lot of Orkeney, disputes his kingship. King Lot dies, however, in a fight with Sir Pellynore, and Arthur solidifies his kingship by marrying Gwenyvere, who brings with her a round table with room for 150, including 100 knights. With Arthur supplying forty-nine more men and a seat left for one as-yet-unknown, the fellowship of the Round Table is born.
And just in time, too, because soon after this, Arthur receives a demand for tribute from Lucius, Emperor of Rome. At the advice of his nobles, he goes to war with him, wins, and becomes emperor of Rome. Nice work, Artie. On his way home, he makes all the lands he passes through become part of his kingdom.
At this point, the story diverges from Arthur to focus on a few of his knights. In "A Noble Tale of Sir Launcelot du Lake," we learn that Launcelot has great success on many quests, and frees some of Arthur's knights from their captivity in the dungeon of an evil knight, Sir Tarquin.
"Sir Gareth of Orkeney" recounts the arrival in Arthur's court one day of a mysterious young man who begins life there as a kitchen knave. This new guy soon proves his worth in a series of battles with a family of knights, through which the lucky duck wins a wife. The young man turns out to be none other than Sir Gareth, Arthur's nephew and the brother of Sirs Gaheris, Aggravayne, and Mordred.
"The Fyrste and the Secunde Boke of Syr Trystram de Lyones" tells the story of Sir Trystram, a Cornish knight whose love for the beautiful Isode gets him into trouble, since she happens to be the wife of his uncle, King Mark – oops.
Finally, the focus returns to Arthur's court with "The Noble Tale of the Sankgreal." Here, Arthur's knights ride off in a search of the Holy Grail, the cup from which Jesus drank at the last supper, which possesses some seriously miraculous powers. All the knights long for even just a glimpse of the Grail, but only Galahad, Percyvale, and Bors – the knights who are chaste and pure, after all – are able to see it.
Launcelot, the "best knight in the world" in all other ways, discovers that the energy he has wasted on earthly glory and love don't do him any good in this spiritual quest, so the Grail is not for him. Yet Launcelot's back in full form with "The Tale of Sir Launcelot and Quene Gwenyvere," in which he successfully defends Gwenyvere against a charge of poisoning and rescues her from the evil clutches of Sir Mellyagaunce. Phew. Never a dull moment in Camelot.
All good things must come to an end, however, and "The Death of Arthur" finds Launcelot and Gwenyvere's illicit love exposed by Sirs Aggravayne and Mordred, who have some seriously sinister motives. Rather than let the Queen be burned at the stake, Launcelot rescues her, accompanied by an alliance of knights who take his side rather than Arthur's.
In the battle to save Gwenyvere, Launcelot accidentally kills Sirs Gareth and Gaheris. These deaths cause Sir Gawain, their brother, to goad Arthur into war with Launcelot, in the hope of avenging them. Arthur and his forces besiege Launcelot's castle in France, leaving England in Sir Mordred's hands. Mordred forges letters claiming that Arthur has died, and declares himself king. Arthur must return to England to take control back from Mordred. Soon after his return, Arthur and Mordred kill one another in the Battle of Salisbury Plain.
But does Arthur really die? The story gets a bit murky at this point, stating that some people believe Arthur is simply in another place, from which he'll eventually return to help England in the crusades. In any case, Queen Gwenyvere blames herself for the fall of the kingdom and takes to a nunnery. Launcelot and his knights follow her lead, and at the end of the book, Launcelot, now a monk and priest, buries Gwenyvere's body next to Arthur's before he dies as well.