The book describes the protracted war between the domineering King Gorice of Witchland and the Lords of Demonland in an imaginary world that appears mainly medieval and partly reminiscent of Norse sagas.

The Worm Ouroboros is written largely in sixteenth-century English, a nearly unique approach among popular fantasy novels; with Eddison making use of his experience translating Norse sagas and reading medieval and Renaissance poetry.

[1] Eddison also incorporated a number of actual early modern poems into the story, including Shakespeare's 18th sonnet, all meticulously credited in an appendix.

His successor (or reincarnation) Gorice XII is a sorcerer who banishes Goldry to an enchanted mountain prison, by means of a perilous sorcery requiring the help of the devious Goblin traitor Lord Gro.

They escape with the aid of La Fireez, the prince of Pixyland and vassal of King Gorice, who helps them at great personal cost because he owes them a debt of honor.

Juss and Brandoch Daha return home to Demonland and then start an expedition to rescue Goldry Bluszco from his terrible prison, somewhere past the mountains of Impland.

From Sophonisba they learn that Goldry is held in prison on the top of Zora Rach Nam, a mountain which cannot be climbed and whose peak is surrounded by unceasing flames.

But matters are not completely hopeless, as one of Queen Sophonisba's martlet scouts has told them of another hippogriff egg lying at the bottom of a lake in Demonland.

A new Witchland army, under the command of Lord Corinius, defeats Spitfire and captures most of Demonland, including Brandoch Daha's castle of Krothering, which had been watched over by his sister Lady Mevrian.

Research done by Paul Edmund Thomas (who wrote an introduction to the 1991 Dell edition) shows that Eddison started imagining the stories which would turn into The Worm Ouroboros at a very early age.

Many people (including J. R. R. Tolkien) have wondered at and criticized Eddison's curious names for his characters (e.g. La Fireez, Fax Fay Faz), places and nations.

According to Thomas, the answer appears to be that these names originated in the mind of a young boy, and Eddison could not, or would not, change them thirty years later when he wrote the stories down.

The tale's morality has also been described as uncommon in modern fantasy; in particular, it differs sharply from Tolkien's heroism of the common man in a fight against evil and C. S. Lewis's Christian allegory.

The leaders of Witchland are regarded as noble and worthy opponents; in the final chapter, Goldry Bluszco compares them very favorably with the "uncivil races" of Impland.

"[6] Reviewing a 1952 edition, Boucher and McComas described it as "one of the major imaginative novels of this century" and "the detailed creation of a vividly heroic alien history."

They particularly commended "the resonant clangor of its prose, the tremendous impetus of its story-telling, [and] the magnificent audacity (and sternly convincing consistency) of its fantasy concepts.

"[7] Donald Barr declared that Eddison wrote "in a heroic prose made of high ceremonial gestures and tropes from the great age of metaphor and described The Worm as being "quite unique among modern novels" as "a narrative of pure event" where, with a lone exception, "we are never given the interior of a character, only the actions".

[8] In 1963, Avram Davidson praised the novel's prose for "abound[ing] in beautiful, quotable language" and its story as one of "war, witchcraft, adventure, conspiracy, violence, bloodshed, intrigue."

"[9] However, J. Max Patrick, also reviewing the Xanadu paperback, dismissed the novel as "a pseudo-Ossianic epic, adolescent in tone and pretentiously archaic", although commenting that "Eddison sometimes achieves the splendid prose and gorgeous artifice appropriate to his sagas.