We recently got done reading Son of a Witch, by Gregory Maguire. It’s the second volume in the series The Wicked Years, which starts with Wicked, presenting some of the backstory behind the rather shallow Oz stories, full of their cardboard-cutout evil characters. They are wonderful stories, although Maguire inserts rather raunchy scenes in them at various places, often for no readily discernible reason, as they often contribute nothing to the the plot.
Maguire is obviously a fan of Baum’s work, as he is very true to the details provided in the original Oz books, while providing a great deal of depth where Baum leaves out details. Often, however, Baum’s easy answers are explained as political lies and propaganda, which is just as delightful.
I highly recommend these books, although you don’t want to read them with your kids.