Eddison was greatly influenced by the classics of Homer, Sappho, Shakespeare, and Webster as well as Norse sagas and French medieval lyric literature. He borrowed fragments from these works unashamedly.
The Worm Ouroboros is an epic tale of heroes and villains bound up in monumental battles in a fanciful world. The worm is a dragon. The scene in which it is conjured is the finest one of its type that I have ever read. You should be left gasping for breath by its end.
The story begins with a curious scene that reveals the narrator at home in England. Disturbed by signs and portents, he retires to a solarium in private while his wife retires to their bedchamber. Alone he is startled awake or deeper into a dream, by a martlet that escorts him via magical carriage to another land, maybe another world. We're not sure which and we never learn. The narrator never again appears in the story as other than a disembodied observer of the characters and their struggles, triumphs, and defeats. Critics have speculated on this opening. Most complain that it is unnecessary. I am more forgiving.
My library, long since destroyed by my first wife, contained a textbook on mythology published in 1814. It began with a lengthy prologue apologizing for it. The author seemed to fear divine retribution for putting such blasphemous words to paper. He assured readers that there was but one true God and that Jesus was his Son. He went on to explain that he wrote the tome only to provide students of literature with these mythological references that they might encounter while reading early literature. He begged God's and the reader's forgiveness, and assured everyone that he did not believe in these pagan things. I suppose that Eddison was doing something of the like in distancing himself from what might be mistaken for pagan sagas.
One last note. Don't skip to the end. Stifle the urge. It is a treat, an unexpected treat. Eddison ended his tale with the most startling twist that I have ever read, and I've read a great many books in almost seventy years.