David Omand and Mark Phythian structure this book as an engaging debate between a former national security practitioner and an intelligence scholar. Rather than simply presenting their positions, throughout the book they pose key questions to each other and to the reader and offer contrasting perspectives to stimulate further discussion. They demonstrate the value for both practitioners and the public of weighing the dilemmas of secret intelligence through ethics. The chapters in the book cover key areas including human intelligence, surveillance, acting on intelligence, and oversight and accountability. The authors disagree on some key questions, but in the course of their debate they demonstrate that it is possible to find a balance between liberty and security. This book is accessible reading for concerned citizens, but it also delivers the sophisticated insights of a high-ranking former practitioner and a distinguished scholar.