Here, the author of the Oz books drops his usual storytelling and creates a myth for Santa Claus, and by connecting it to Oz later, reveals the hierarchy of Immortal beings who could also exist in Oz.
There be spoilers ahead!
The book opens by introducing the Forest of Burzee, which Baum would use in later novels and short stories. (And by association, all of these would be connected to Oz.) Maps of Oz show it to be just across the Deadly Desert from the Quadling Country, so perhaps Glinda is familiar with some of the Immortals there?
Now, we begin meeting the Immortals: we have the nymphs, who care for trees, Ryls, who care for plants, especially flowers, then the Knooks who care for animals.
We focus on one nymph in particular: Necile. Having the responsibility of caring for certain trees in Burzee has grown tiresome for her, as her trees are now strong and need little protection. Now that she has little to do, Necile begins to long for something new to do.
The Great Ak, Master Woodsman of the World, visits Burzee for Budding Day and tells the nymphs about the lives of humans. He tells them how neglected children are and mentions he had found a baby just outside of Burzee. Leaving it with Shiegra the lioness, he commanded that no animal harm it.
Necile is fascinated by the story and goes to see the baby. She feels compassion for it and brings it back to Burzee with her. Ak eventually decides to let Necile care for the baby, who she names Claus, meaning "Little One."
Baum created with Ak and Necile and the Nymph Queen Zurline (not to be confused with Lurline) almost like gods from mythology, except now, they actually have compassion for mankind. Instead of interfering and causing pain for mankind, they help when they choose to (Ak tells about how he started a small bonfire to keep some freezing children warm until their parents returned home).
Claus' life in Burzee is related briefly, until he gets to be a responsible age. Then Ak takes him on a journey around the world so he can see his own kind first hand. Claus feels compassion for children and mankind in general, and the deepest conversation in all of Baum's fantasies ensues:
"Then why, if man must perish, is he born?" demanded the boy.After this journey, Claus determines to bring happiness to children. All the Immortals pledge their aid to him, and Ak guides him to the Laughing Valley, where he decides to make his home. However, being a friend of the Immortals has its benefits, for while Claus sleeps, they build him a home from logs he collected, and bring him food when he needs it so he can focus on what he has determined to do.
"Everything perishes except the world itself and its keepers," answered Ak. "But while life lasts everything on earth has its use. The wise seek ways to be helpful to the world, for the helpful ones are sure to live again."
Claus visits nearby towns and plays with children. The joy he brings to children brings joy to their parents.
However, winter prevents Claus from making more visits, so he spends it at home with his cat, Blinkie. To pass the time, Claus begins whittling at a piece of wood and it ends up turning into an image of Blinkie.
Shortly afterward, Claus hears a cry for help outside, and finds a young boy in the snow. He brings him home and nurses him back to health. The boy, Weekum, wants to play with Blinkie, but Blinkie isn't a playful cat. So Claus lets him play with the wooden cat, and then lets him keep it. Seeing how much Weekum liked the cat, Claus decides to make more for children everywhere. The Ryls, when they visit, decide to give Claus paint to color the wooden cats with.
The toy cats become popular with the children, and Claus makes more. Shiegra the lioness visits in her old age (a reminder that Baum drops that mortal beings do grow old and die), and Claus carves a special image of her, looking fierce and proud. When he tries to give this to two children, they are scared and run, so he resolves only to make toys of friendly animals. Later, when a rich lord's daughter visits him, he realizes that even children in rich families were no happier than the poor, so he makes a doll of clay based on Necile for her. This gives Claus more toys to make, and the children become happier.
By protecting and aiding Claus, the Immortals have made him almost one of them. It is now Claus who will visibly assist mankind.
Now, Baum gives us the antagonists, which he states he wishes he could overlook. The Awgwas, cruel beings that are not immortal, and cannot be seen by humans, but they can influence them to do wrong. Claus' work with the children breaks their hold over them, and the Awgwas are not happy at all.
The Awgwas start interfering with Claus, and send him to a distant country. However, using the secret words of the Ryls, he is transported back home. He is kidnapped again and hidden in the mountains of the Awgwas (which are not depicted on any map, but I'd imagine them being a bit south of the Laughing Valley, near the shore; I later thought that maybe now certain Jackdaws make their home there), but again the fairies rescue him. So, they attack Claus when he attempts to visit children and steal the toys. Finally, Claus stays at home and makes toys and fills his shelves with them, but when the shelves are full, Claus becomes sad and visits Ak.
Ak tells the Awgwas to leave Claus alone, but they refuse, so Ak declares war. The Nymphs, Ryls, Knooks, and Fairies join Ak against the Awgwas, the Three-Eyed Giants of Tatary, Asiatic Dragons, Black Demons, and Goozzle-Goblins. Despite Ak's army being outnumbered, they win, because it is a law that the powers of Evil cannot withstand Good. Thus, Ak is happy to assure Claus (and likewise, Baum his readers) that Awgwas are dead and are no longer to be feared.
Once again, Claus is unable to visit children during winter, but when he notices how easily Flossie and Glossie the deer can walk over frozen snow, he sends them to ask Will Knook for permission to draw a sledge so they might carry Claus to homes of children. Peter agrees, only if the delivery is made at night and the deer return to the forest by day. On his journey, Claus finds doors locked, so he uses chimneys to enter.
When people find the toys, they call Claus a saint, which is how "Santa" became prefixed to his name. (Santa Claus, by Baum, means "Saint of Little One.") Will Knook, however, notices that his deer were exactly one minute late in returning, so Claus begs Ak that the deer not be punished. The Nymphs, Ryls, and Fairies offer gifts to any deer that will assist Claus if Will and the King of the Knooks will allow the deer to continue to assist Claus. They agree, on condition that Claus makes one annual trip, and they set it on Christmas Eve.
Claus attempts to make more toys in time for Christmas Eve, but cannot make many, but fortunately, the Fairies find the toys the Awgwas stole and bring them to Claus so he can distribute them.
In building his new sledge, Claus trades with the Gnome King (whether or not he is the same Nome King of Ozma of Oz is a matter of debate) for runners and strings of bells for the deer. The Fairies get candies and fruits to fill stockings with and to decorate Christmas trees with (both traditions get set up in the story).
And here, Baum did his first crossover. The Fairies bring the candy from Phunnyland, which Baum later re-wrote into the Valley of Mo. (Or maybe, in the terms of the fictional world, they changed their name.) When Oz became linked with Baum's version of Santa Claus (in Queer Visitors from the Marvelous Land of Oz and The Road to Oz), so did Mo. (So was Queen Zixi of Ix.)
Claus continues his work for many years, until he ages and tires, and one day, he goes to lie down, and the Immortals realize he is about to die. Quickly calling all the Immortals, Ak proposes that Claus be given the Mantle of Immortality, which will make him Immortal. After a short conversation, all the Immortals agree, and they use the Mantle to drive the Spirit of Death away from him forever.
As Claus lives on, the world changes, and he finds chimneys have changed. Confused by stove chimneys, he brings along his three Immortal assistants, Kilter, Nuter, and Wisk, who'd been helping him make toys. They help him get into the homes of everyone, and soon, Santa must deputize every parent to help him.
So, to lighten his task, which was fast becoming very difficult indeed, old Santa decided to ask the parents to assist him.There are increasingly more children, but Santa doesn't mind as long as he has help.
"Get your Christmas trees all ready for my coming," he said to them; "and then I shall be able to leave the presents without loss of time, and you can put them on the trees when I am gone."
And to others he said: "See that the children's stockings are hung up in readiness for my coming, and then I can fill them as quick as a wink."
And often, when parents were kind and good-natured, Santa Claus would simply fling down his package of gifts and leave the fathers and mothers to fill the stockings after he had darted away in his sledge.
"I will make all loving parents my deputies!" cried the jolly old fellow, "and they shall help me do my work. For in this way I shall save many precious minutes and few children need be neglected for lack of time to visit them."
"In all this world there is nothing so beautiful as a happy child," says good old Santa Claus...
Some critics have pointed out that for the titular character, Claus doesn't do much. Admittedly, this is true. It is the life of someone who took on a mighty task and how he accomplished it, and who assisted him. Rather than write thrilling adventures for Santa, Baum chose instead to build a mythology around the character and the symbols connected with him. Baum's pseudonymous work shows he was capable of thrilling adventures, but he decided to go for a quieter tale that felt magical.
And in the end, it works. Aside from The Wonderful Wizard of Oz and The Marvelous Land of Oz, it is probably the most often-adapted book by Baum. There's been a television special, an anime television series, two animated movies on video, a graphic novel, and even this year an abridgement with new illustrations.
Baum made Santa Claus his own character, a kind man who took delight in pleasing children, a description that best fits this wonderful character, and the man who wrote the biography.