During a twister, Dorothy is hit on the head by a gate and once again whisked away to the land of Oz. But this time, on her way to the Emerald City, she discovers a terrible plot by the witch Mombi to conquer Oz with an army of monster green elephants that's she's brewing up. She escapes with the help of Mombi's slave Pumpkinhead, and, together, they try to warn King Scarecrow and her other friends that Mombi is coming, but she finds that her friends haven't quite changed as much as she thought. So it's up to her, Pumpkinhead, and the living carousel horse Woodenhead to find a way to stop Mombi's Green Elephants...