This work investigates the motivations and operational success of Kim Philby, the most notorious double agent of the twentieth century, to determine how he maintained his cover within British intelligence for decades. The authors, Bruce Page, David Leitch, and Phillip Knightley, utilize extensive investigative journalism and primary source interviews to reconstruct Philby's career. They argue that his betrayal was not merely a personal failing but a systemic collapse of the British establishment's class-based security apparatus. The text provides a detailed examination of the geopolitical climate that allowed a Soviet mole to rise to the highest levels of MI6.

Experts and historians frequently cite this text as a foundational account of the Philby affair due to its proximity to the events described. Readers often note the dense, investigative prose style that reflects the journalistic standards of the late 1960s.