L. Frank Baum 
Glinda of Oz 

In L. Frank Baum’s "Glinda of Oz", (1920) Glinda and Dorothy travel to an obscure corner of Oz to prevent a war between the Skeezers and the Flatheads. When the Skeezers imprison them on a glass covered island at the bottom of a lake, Glinda and Dorothy must call upon their magical friends to rescue them. The 14th in the Oz series, it was the last of the original Oz books written by L. Frank Baum and was dedicated to his son Robert.