Purports to be a biography of Walsingham, with emphasis on his career as statesman, diplomat, and, like it says, spymaster. Disappointingly, never really gets into the details of Elizabethan espionage: we get many many names and outlines of plots, but not enough specifics especially on how we know these things now. Nicholl's "The Reckoning" is far the better book for that sort of thing--and for that matter, how can Budiansky include "The Reckoning" in his bibliography, and then mention Marlowe just once to say "maybe" he was a spy?!? Anyway, without these sort of details the book is mostly just an overview of the big international incidents of the time--the St. Bartholomew's Day Massacre, the story of Mary Queen of Scots, and the Spanish Armada--with Mr. Secretary as the point of continuity. The author has drawn as much as he can from Walsingham's papers, but Mr. Secretary was such a private reserved man that even working from these sources--correspondence, notes and memoranda, stuff like that--we don't get much about his thoughts, his feelings, his reactions, just what happened around him. Also, chapters are thematic more than chronological, so there's overlapping instead of a straight story.
A pleasant, easy read, but two more points show how very much this is not a scholarly work: no index(!), and the "Other books by the author" list has nothing else Elizabethan, but a series of titles like "The Character of Cats," "The Truth About Dogs," "If a Lion Could Talk," and "The World According to Horses." So, fun and interesting to read, but it is not a work of historical scholarship by any means.