L. Frank Baum 
The Lost Princess of Oz (Illustrated) [EPUB ebook] 

When Princess Ozma mysteriously disappears, four search parties are sent out, one for each of Oz’s four countries. Most of the book covers Dorothy and the Wizard’s efforts to find her. Meanwhile, Cayke the Cookie Chef discovers that her magic dishpan (on which she bakes her famous cookies) has been stolen. Along with the Frogman, they leave their mountain in Winkie Country to find the pan.