Mathew Sadler has put more thought and creativity into this beautifully written chess book than several chess authors combined. He is a deep and original thinker, having returned to the echelons of top level chess after a break (and a career in finance).

He was famous for his Book Reviews in New in Chess, which showed a profound understanding of the game. His reviews would be discursive. He would present game fragments from his and other players' praxis before returning to the book being reviewed.

He uses a similar approach in this focused book sure to help a advancing player with a good grasp of theory find a repertoire and a plan.

His book is extremely well organized in thought into the following chapters.

1)How discovering ideas in the openings is not a matter of switching on an engine or a database, he explains analyses for a person with an already broad exposure to openings as he makes observations about recurring patterns (such as g5 pushes to secure outpost for Knight on e5) in different middle games from different openings.

2) Introducing new ideas into YOUR openings, a chapter on how you make an opening your own, (as some wit wrote some years ago, it is not that we are too good for the Ruy Lopez, it is that the Ruy Lopez is too good for us). He addresses several emotional attachments to openings that lose you points ( I paraphrase freely), and emphasises technical aspects of openings. How he analyzed the Dutch, showing several games from his own as well as Yusupov's praxis.

3) Playing Unorthodox Openings is perhaps the fairest look at offbeat openings at high level you are ever likely to see. It is not all a bed of roses. Yet, players like Speelman, Sadler, and in our times Nakamura have the nerve to play offbeat openings. What do they get out of it? Here is a good look. The English opening (..b6 and ..e6, with interesting theoretical lines) is amply supported with examples, and to a lesser extent the Pirc/modern complex.

4) Types of thinking in Middlegames is a 16 page essay with exercises that owes much to Dvoretsky. 4 types of thinking. Really useful to guide your choice of plan. These are the sort of stuff not every book talks about. THis is the kind of thing that makes this book a keeper (along with your first My System, or Pawn Power in chess, except this is way more advanced).
Finally 5) and 6) are That Didn't quite work out and Thinking in Endgames. ( )