The story starts in the final years of the rule of King Uther Pendragon. The first part, "The Sword in the Stone", chronicles Arthur's upbringing by his foster father Sir Ector, his rivalry and friendship with his foster brother Kay, and his initial training by Merlyn, a wizard who lives through time backwards. Merlyn, knowing the boy's destiny, teaches Arthur (known as "Wart") what it means to be a good king by turning him into various kinds of animals: fish, hawk, ant, goose, and badger. Each of the transformations is meant to teach Wart a lesson, which will prepare him for his future life.
Merlyn instills in Arthur the concept that the only justifiable reason for war is to prevent another from going to war and that contemporary human governments and powerful people exemplify the worst aspects of the rule of Might.
White revised the original Sword in the Stone heavily for the four-part book in 1958. He took out the wizards' duel between Merlyn and Madame Mim, the adventure with T. natrix the snake, and the episode with the giant Galapagas. The first of those was replaced with the adventure of the ants. In Wart's adventure with Merlyn's owl, Archimedes, the boy Arthur becomes a wild goose instead of visiting the goddess Athena. In the adventure with Robin Hood in the original book, the outlaws take the boys to attack the Anthropophagi (cannibals) and Wart kills a Sciopod. In the 1958 version, the boys lead an attack on Morgan le Fay's Castle Chariot and Kay kills a griffin. The revisions reflect White's preoccupation with political questions in The Once and Future King, and generally give the first part of the work a more adult flavour.
In part two, The Queen of Air and Darkness, White sets the stage for Arthur's demise by introducing the Orkney clan and detailing Arthur's seduction by their mother, his half-sister Queen Morgause. While the young king suppresses initial rebellions, Merlyn leads him to envision a means of harnessing potentially destructive Might for the cause of Right: the chivalric order of the Round Table.
The third part, The Ill-Made Knight, shifts focus from King Arthur to the story of Sir Lancelot and Queen Guinevere's forbidden love, the means they adopt to hide their affair from the King (although he already knows of it from Merlyn), and its effect on Elaine, Lancelot's sometime lover and the mother of his son Galahad.
The Candle in the Wind unites these narrative threads by telling how Mordred's hatred of his father and Sir Agravaine's hatred of Lancelot cause the eventual downfall of Arthur, Guinevere, Lancelot, and the entire ideal kingdom of Camelot.
The book begins as a quite light-hearted account of the young Arthur's adventures and King Pellinore's interminable search for the Questing Beast. Parts of The Sword in the Stone read almost as a parody of Arthurian legend by virtue of White's prose style, which relies heavily on anachronisms. However, the tale gradually changes tone: The Ill-Made Knight becomes more meditative, and The Candle in the Wind finds Arthur brooding over death and his legacy.
