A Plague of Wizards is the eighth book in The Sorceress and the Dragon series (formerly Senta and the Steel Dragon). The book started with what if Senta disappeared for several years and what would happen to Port Dechantagne and the people in it if that happened.
The question that naturally follows is where was she and what happened to her. I guess a lot of that part of the story comes from my reading books and watching movies about people who have been mistreated in mental institutions.
There are a number of story elements that result from this book, particularly with Senta and Baxter that continue to the end of the series.