The Queen's Agent: Francis Walsingham at the Court of Elizabeth I

There were many flamboyant and charismatic figures at the Elizabethan Court, but Francis Walsingham was not one of them. Pessimistic and puritanical, a tireless administrator and notorious spymaster, he is often portrayed as a dour, sinister figure. Biographer John Cooper cannot deny that Walsingham was a pessimist, but nonetheless manages to make him human, skilfully placing him in context in an age of such discord and danger that by the end of the book we share the poor man's unceasing anxiety for his queen, his country and his religion.

The reign of Elizabeth I is the stuff of which myths and Hollywood blockbusters are made, but the beguiling pictures of "Gloriana" ruling benignly over a peaceful realm are a long way from the brutal realities of the time. As Walsingham saw only too well, Elizabeth was in constant danger, as an unmarried, childless, Protestant queen of a land riven with religious disagreements. Her life was threatened by rebellion and plots at home and invasion from abroad. If she married, she risked political disaster and death in childbirth; if she didn't, a disputed succession threatened civil war. Assassination was a constant fear. Elizabeth herself was also a source of anguish; Walsingham not only lamented "the sores of this diseased state" but expressed his exasperation at "seeing her majesty bent rather to cover than to cure them".

Walsingham's lifelong struggle against the Catholic threat begins to make more sense when we realise that he was in Paris in 1572 during the St Bartholomew's Day Massacre. The city was consumed by violence, "of which most horrible spectacle I was an eye witness", he later wrote. Two thousand Protestants were slaughtered; the Seine was full of butchered corpses. "They spared not the aged, nor women, nor the very babes," wrote one account. Walsingham lived through it all, holed up with his small daughter and his pregnant wife, and he never forgot.

His network of spies and informers contained some unedifying characters; he tortured his suspects, and condemned them willingly to the horrors of a traitor's death, but having read this book, it is easier to understand the powerful compulsion that spurred him on. "Above all things," he wrote, "I wish God's glory and next the queen's safety."

The man who emerges from this detailed, insightful and highly readable account is not entirely likeable, but he does compel our compassion. Elizabeth, and his own unwavering sense of duty, worked him literally to death. Attempting to resign in the throes of his last fatal illness, he was instructed by the queen to continue making "speedy despatch" of business concerning Ireland, until she found a replacement.

He was also much more complicated a character than is usually appreciated: educated, cosmopolitan, and a lover of falconry, gardens and music. He had an eye for detail, in an age when encrypted messages could be conveyed written on the inside of an unbroken eggshell, but he also had a grasp of the international stage, promoting trade with Muscovy, diplomatic links with the Ottoman Turks, and the settlement of Virginia. The story of his life is also the story of Elizabeth, of Mary Queen of Scots, of the religious conflicts that savaged Europe, and the extraordinary world of Tudor espionage. Efficient, ingenious, devout and anxious, Walsingham was at the heart of it, labouring to keep his queen and his faith alive.