Ojo the very unlucky, is a young Munchkin boy who, devoted to life with his uncle Unc Nunkie in the wilderness but on the verge of starvation, goes to see a neighboring "magician" and old friend of Unc, Dr. Pipt. While there they see a demonstration of the Pipt-made Powder of Life, which animates any object it touches after saying the magic words. Unc Nunkie and Dr. Pipt's wife are also the sufferers of the consequences of another of the Doctor's inventions, the Liquid of Petrifaction, which turns them into solid marble statues.
The remainder of this book is Ojo's quest through Oz to collect the five components of an antidote to the Liquid: a six-leaved clover found only in the Emerald City, three hairs from the tip of a Woozy's tail, a gill (a quarter of a pint) of water from a dark well (one that remains untouched by natural light), a drop of oil from a live man's body, and the left wing of a yellow butterfly. With the help of the life-size patchwork doll named Scraps, Bungle the snobbish Glass Cat (another of Dr. Pipt's creations), the Woozy, Dorothy, the Shaggy Man, and the Scarecrow, Ojo gathers all of these supplies but the left wing â the Tin Woodman, who rules the yellow Winkie Country, which is the only place where yellow butterflies grow, will not allow any living thing to be killed, even to save another's life.
The party returns to the Emerald City, where the Wizard of Oz (one of the few allowed to lawfully practice magic in Oz) uses his own magic to restore Unc Nunkie and Dr. Pipt's wife. The story is also a growth process for Ojo; he learns that luck is not a matter of who you are or what you have, but what you do; he is renamed "Ojo the Lucky," and so he appears in the following Oz books.

Question: Who rules the yellow Winkie Country?
Answer: The Tin Woodman.
Alternative answer: the Tin Woodman