After "the wizard of Oz", Dorothy is sent a key from Oz, on a shooting star,
Aunt Em takes Dorothy to see a doctor, who tries a strange electrical experiment to rid her of memories of Oz.
Dorothy escapes, with her chicken Billina. They fall into a river in a storm: Dorothy climbs onto a wooden crate, and falls asleep. The crate drifts into a pond in the deadly desert which surrounds Oz.
Dorothy and Billina discover the yellow brick road, and make their way to the Emerald City. They find it in ruins, and all the people in it turned to stone: including some headless dancing girls, the tin man, and the cowardly lion. They meet the nasty "wheelers": humanoids with wheels instead of hands and feet, who chase Dorothy into a dark passage. At the end of the passage, there is a door, which Dorothy unlocks with the key she was sent.
In the room beyond, they find "Tik Tok", a clockwork robot. Dorothy winds him up, and they go and fight the wheelers. They go into a tower, and find Mombi, a sinister woman with a removable head, and a gallery of other heads. Mombi captures Dorothy, and imprisons her in the top of the tower: there she meets Jack Pumpkinhead. While Mombi is asleep, they escape from the room. Dorothy steals Mombi's "powder of life", and they use it to build a flying sofa, to escape.
They fly to the mountain of the Nome King, who is now controlling Oz, and has turned everyone to stone. The scarecrow is under his control, apparently turned into an ornament. The king invites them in turn to guess which ornament is the scarecrow: all of Dorothy's friends fail, and so become ornaments themselves.
When it's Dorothy's turn, the king shows her how he now has the ruby slippers, and had used them to conquer the Emerald City. Dorothy goes to make her guess, and guesses correctly. They manage to rescue everyone else, while the king, now transformed into a furious giant, tries to eat everyone. But Billina, who is hidden in Jack's pumpkin head, lays an egg, which poisons the king.
Dorothy then uses the ruby slippers, to put all to rights (see ending).