As we saw at the end of The Emerald City of Oz, L. Frank Baum attempted to end the Oz series through a final chapter where he receives a letter from Dorothy saying goodbye forever as Oz has been magically cut off from the rest of the world in order to protect it from outsiders. However, Baum ran into financial difficulty, and decided to revive the Oz series three years later with The Patchwork Girl of Oz (1913).
And how did he hear this story from Dorothy, after all contact had been so abruptly cut off? Why, through the wonder of science, of course!
The children who had learned to look for the books about Oz and who loved the stories about the gay and happy people inhabiting that favored country, were as sorry as their Historian that there would be no more books of Oz stories. They wrote many letters asking if the Historian did not know of some adventures to write about that had happened before the Land of Oz was shut out from all the rest of the world. But he did not know of any. Finally one of the children inquired why we couldn't hear from Princess Dorothy by wireless telegraph, which would enable her to communicate to the Historian whatever happened in the far-off Land of Oz without his seeing her, or even knowing just where Oz is.
That seemed a good idea; so the Historian rigged up a high tower in his back yard, and took lessons in wireless telegraphy until he understood it, and then began to call "Princess Dorothy of Oz" by sending messages into the air.
Now, it wasn't likely that Dorothy would be looking for wireless messages or would heed the call; but one thing the Historian was sure of, and that was that the powerful Sorceress, Glinda, would know what he was doing and that he desired to communicate with Dorothy. For Glinda has a big book in which is recorded every event that takes place anywhere in the world, just the moment that it happens, and so of course the book would tell her about the wireless message.
And that was the way Dorothy heard that the Historian wanted to speak with her, and there was a Shaggy Man in the Land of Oz who knew how to telegraph a wireless reply. The result was that the Historian begged so hard to be told the latest news of Oz, so that he could write it down for the children to read, that Dorothy asked permission of Ozma and Ozma graciously consented.
So via telegraph, we learn about the story of Ojo and Unc Nunkie -- two Munchkins who live by themselves in an isolated forest. The only problem is, they have run out of food. They decide to leave their home and travel to the Emerald City where they can start a new life and have enough to eat. On their way, they stop by the house of Dr. Pipt, a magician who also lives in the woods with his wife. This is the same magician that invented the Powder of Life that brought Jack Pumpkinhead, the Saw Horse, and the Gump to life in The Marvelous Land of Oz. Even though he is forbidden to practice magic, Dr. Pipt has been working for six years to make some more Powder of Life in order to bring a human-sized patchwork doll that his wife made to life so that it can be their servant and do all the housework.
Just before the powder is ready, Dr. Pipt's wife, Margolotte, picks out the right combination of brains to suit her servant (a bunch of Obedience, some Amiability, a little Truth, and a dash of Cleverness --she wants her to have enough brains to be a good servant, but not so many that she gets any ideas of not obeying her mistress). Ojo thinks that the Patchwork Girl ought to be given as many brains as anyone else, so when Margolotte is helping her husband, he adds in some more of everything, plus Judgment, Courage, Ingenuity, Learning, Poesy and Self-Reliance.
Sadly just as the now very precocious Patchwork Girl is brought to life, a vial of Liquid of Petrification falls on Unc Nunkie and Margolotte and turns them into stone. The magician can make a potion to heal them, but to do it, Ojo will need to go on a journey and collect a six-leaved clover found only in the Emerald City, three hairs from the tip of a Woozy's tail, a gill of water from a dark well, a drop of oil from a live man's body, and the left wing of a yellow butterfly. He takes the Patchwork Girl and a rather stuck-up glass cat that the magician had brought to life earlier and heads out on his journey.
The group meets up with The Shaggy Man, who introduces them to the Scarecrow (who immediately falls head over heels for the Patchwork Girl), the Tin Man, Dorothy, and the rest of the gang. Many adventures are had, and although they aren't able to get all the ingredients for the potion (the Tin Man won't let anybody harm the yellow butterflies that are found only in his kingdom because his heart is too big to see any living thing harmed in any way), everything works out fine in the end.
This is one of the Oz books that was made into a movie produced by Baum in 1914, and if IMDB is to be believed, it is one of the most faithful adaptations.
[And as always, you can read the whole thing online here.]