The book has its flaws: it overplays the closeness of its subjects’ personal relationship and has a tendency – not unusual in dual biographies – to bounce around the chronology; it also includes too many long and undigested extracts from primary documents. Yet at its heart is a fascinating story, well told, of how one idealistic master spy and double agent caused serious damage to the strategic interests of the West; and how another, taught by the first and vehemently anti-Communist, tried to prevent such a betrayal from ever happening again.