We just returned from Russia when my father gave me this book, and said, 'read it'. That was good advice.
Returning from an extended period in a foreign country can be a difficult experience. This book describes problems you can fall into, and how to avoid them.
It talks about how people fail to notice you've even been gone. Or don't seem to care that much what you did. When you understand these are common experiences, it helps those problems become a lot less personal.
Overall, we've applied the principles of this book, and haven't experienced most of the 'reverse culture shock' that many do. And we've been home nearly a year now, so we'll probably do okay.
Good book to give a returning, or retiring missionary, as a gift.