While Dorothy and Ozma are visiting the good witch Glinda, they hear that the Skeezers and the Flatheads are preparing to go to war against each other in a remote corner of Oz. The girls try to thwart this plan, but end up being imprisoned on an island underneath a lake.
This was Baum's last book and he has almost every character he can think of in on the rescue of the girls, although most of them don't really do much but make an appearance.
We are introduced to a few new characters and there is plenty of magic to go around.
This book was published posthumously after Baum died in Hollywood in 1919 when his weak heart finally caught up with him. Ruth Thompson took over the series and went on to publish quite a few more books in the series.
