The first thing you need to know is that the book, even with the Appendix, is only 56 pages long. The second thing to know is that two out of three remarriages that come with children fail.
The author begins with "Welcome to a whole new world - you're a stepmom now." This situation is increasingly common in modern society and, according to the author, most of the issues come from the mother of the kids, not the kids themselves. The purpose of the book is to help the stepmom deal with the kids and their mother.
The Ten Chapters each cover a basic step such as: Understand Her Motives, Refute Don't Retaliate, Give Yourself Space and Help your Husband.
Each chapter concludes with an Action Plan - something you should do today and things you should do every day. For example, in Chapter 2 about Understanding her Motives, Today's Plan says you should (among other things) "Take a moment to look at mom through a different lens."
The Every Day tasks include "Realize that the kids are dealing with mom's behavior as much as or more than you are. How can you help shelter them from a fight that isn't theirs?"
There is varied advice just as there are varied relationships between stepmoms and moms. Some situations can be treated with understanding while others may need legal or other professional assistance.
The Appendix includes Stepfamily Organizations and resources for Parental Alienation Syndrome.
It's Not My Stepkids--It's Their Mom! is a short book but covers an increasing common potential problem.