..Gray's book is an analysis of Berlin's thought and I found it invaluable in organizing my ideas on his philosophy. Gray focuses again and again on Berlin's view that values are often incommensurable (They cannot be ranked against each other) and in addition may also conflict. He describes Berlin's liberalism as agonistic because in making choices human beings sometimes have to decide not between good and evil, but between options which both contain good values, these being in conflict with each other. Gray believes this line of thinking undermines a great deal of traditional liberal thought and also tries to bring out the tensions in Berlin's writing. If you are interested in Berlin I would recommend that you read a few of Berlin's essays before reading this book. His essay "The Originality of Machiavelli" is a good place to start and can be found in a number of different books of his essays such as "The Proper Study of Mankind". I would also like to point out that this book is not a biography of Berlin but a study of his ideas. Michael Ignatieff has written a fairly chunky biography. However, I suspect that Berlin himself would have hoped that people get to grips with his ideas rather than read about his life, interesting though it no doubt was.
Having read other scholars' comments on Gray's interpretation of Berlin's thought, I was intrigued to read this book myself. I can honestly say it is a thoroughly interesting read. Those interested in Berlin and Gray's thought will find this book insightful. Even though Gray's handling of Berlin is questionable in terms of the limits he places on rationalism, he does provide the reader with a detailed account of the origins of Berlin's thought. Finally, the new introduction for this 2013 edition demonstrates the relevance of Berlin's thought, but also provides and insight into Gray's political philosophy.