The book is a collection of Block’s essays on the subject of blackmail — specifically, why he believes it should be legal as a matter of libertarian principle — including rebuttals of many other scholars’ opinions. It’s the most thorough libertarian treatment of this subject that has ever been published or, I am confident, ever will be. And because it’s from Block, it’s a great read besides.
As I say in a blurb on the book’s back cover: “If you want to understand the libertarian position on blackmail, read this book. If you’ve taken it for granted that we need laws against blackmail, Walter Block will challenge your assumptions with provocative arguments you’ll find difficult to refute.”