"Glinda of Oz" by L. Frank Baum is a children's novel published in 1920. The fourteenth and final book in Baum's original Oz series follows Princess Ozma and Dorothy as they journey to a remote corner of Oz to prevent war between the Flatheads and Skeezers. When their peace mission fails and they become trapped underwater on a magically submerged glass island, Glinda must lead a rescue expedition to free them before it's too late. (This is an automatically generated summary.)
These books are free to read. Each is in the public domain in the United States; check your own country's rules before you copy or share one.