Dorothy is an orphan raised by her Uncle Henry and Aunt Em in the bleak landscape of a Kansas farm. She has a little black dog Toto, who is her sole source of happiness. One day the farmhouse, with Dorothy and Toto inside, is caught up in a cyclone and deposited in a field in Munchkin Country in the Land of Oz. The falling house kills the ruler of the Munchkins, the Wicked Witch of the East.
The Good Witch of the North comes with the Munchkins to greet Dorothy and gives Dorothy the silver shoes that the Wicked Witch of the East had been wearing when she was killed. In order to return to Kansas, the Good Witch of the North tells Dorothy that she will have to go to the "Emerald City" or "City of Emeralds" and ask the Wizard of Oz to help her.
On her way down the yellow brick road, Dorothy frees the Scarecrow from the pole he is hanging on, restores the movements of the rusted Tin Woodman with an oil can, and encourages them and the Cowardly Lion to journey with her and Toto to the Emerald City. The Scarecrow wants to get a brain, the Tin Woodman a heart, and the Cowardly Lion, courage. All are convinced by Dorothy that the Wizard can help them too. Together, they overcome obstacles on the way including narrow pieces of the yellow brick road, Kalidahs, a river, and the Deadly Poppies.
When the travelers arrive at the Emerald City, they are asked to use green spectacles by the Guardian of the Gates. When each traveler meets with the Wizard, he appears each time as someone or something different. To Dorothy, the Wizard is a giant head; the Scarecrow sees a beautiful woman; the Tin Woodman sees a ravenous beast; the Cowardly Lion sees a ball of fire. The Wizard agrees to help each of them, but one of them must kill the Wicked Witch of the West who rules over the Winkie Country.
As the friends travel across the Winkie Country, the Wicked Witch sends wolves, crows, bees, and then her Winkie soldiers to attack them, but they manage to get past them all. Then, using the power of the Golden Cap, the Witch summons the Winged Monkeys to capture Dorothy, the Cowardly Lion and Toto, and to destroy the Scarecrow and the Tin Woodman.
When the Wicked Witch gains one of Dorothy's silver shoes by trickery, Dorothy in anger grabs a bucket of water and throws it on the Wicked Witch, who begins to melt. The Winkies rejoice at being freed of the witch's tyranny, and they help to reassemble the Scarecrow and the Tin Woodman. The Winkies love the Tin Woodman, and they ask him to become their ruler, which he agrees to do after helping Dorothy return to Kansas.
Dorothy uses the Golden Cap to summon the Winged Monkeys to carry her and her companions back to the Emerald City, and the King of the Winged Monkeys tells how he and the other monkeys were bound by an enchantment to the cap by Gayelette.
When Dorothy and her friends meet the Wizard of Oz again, he tries to put them off. Toto accidentally tips over a screen in a corner of the throne room, revealing the Wizard to be an old man who had journeyed to Oz from Omaha long ago in a hot air balloon.
The Wizard provides the Scarecrow, the Tin Woodman, and the Cowardly Lion with a head full of bran, pins, and needles ("a lot of bran-new brains"), a silk heart stuffed with sawdust, and a potion of "courage", respectively. Because of their faith in the Wizard's power, these otherwise useless items provide a focus for their desires. In order to help Dorothy and Toto get home, the Wizard realizes that he will have to take them home with him in a new balloon, which he and Dorothy fashion from green silk. Revealing himself to the people of the Emerald City one last time, the Wizard appoints the Scarecrow, by virtue of his brains, to rule in his stead. Dorothy chases Toto after he runs after a kitten in the crowd, and before she can make it back to the balloon, the ropes break, leaving the Wizard to rise and float away alone.
Includes a biography of the Author