Based on extensive research, Piers Blofeld builds the vivid and compelling proposition that Anthony Blunt was not simply "the fourth man" in the infamous Cambridge spy ring, but actually the greatest spy-master of all. The discovery of a mysterious Agent Josephine in new archive material suggests an almost limitless treachery, towards both friends and country alike. Blunt's treason led to the deaths of tens of thousands of people and shaped post-second world war history.

This is not a biography but a re-examination of the series of events that start in the mid-1930s, encompass the Second World War where Blunt was not only advising Churchill but reporting to Stalin, and possibly the German High Command, and finally leads us to Guy Burgess and Donald Maclean's defection to Russia in 1951.

Blunt managed to sustain his brilliant career as an art historian, Keeper of the King's and then the Queen's pictures and subsequently Knight of the Realm. Meanwhile, he stayed in the shadows, protected by his many friendships with the great and the good. Blunt was more than happy to let others take centre stage, but was this part of a bigger plan?

The Master reads like the best of spy-stories and here the old adjunct is a true one: "you couldn't make it up".