This is a book on reducing moves. It has a chapter on the basics, three chapters on reducing joseki, a chapter on attack and defense, and a chapter of problems. As such, it's both a book about the middle game and a dictionary, but since the heart of the book is the reducing move josekis and since those take up more than half of the pages, it mostly feels like a dictionary to me. You might want to read the first chapter when you're reading intermediate books, and then ignore the other chapters until you're more advanced except when you want to refer to it to answer a question about a position that occurred in your game. It's probably a pretty good book, considered as a dictionary; I haven't had much reason to refer to it, so I can't really say.