Books
(these are Amazon affiliate links – you pay the same price, but the podcast gets part of the profits. Hooray!)
The Queen’s Agent by John Cooper
The Watchers by Stephen Alford
Burghley: William Cecil at the Court of Elizabeth I by Stephen Alford
Her Majesty’s Spymaster: Elizabeth I, Sir Francis Walsingham, and the Birth of Modern Espionage by Stephen Budiansky
Other Englandcast Episodes you might enjoy:
Episode 085: Tudor Times on Mary Queen of Scots
Throwback Episode 027: Francis Walsingham, Spymaster
The Spanish Armada Part I: A 30 Year Road to Battle
The Tudor Times Resources on Francis Walsingham
http://tudortimes.co.uk/people/francis-walsingham-life-story
The Allegory of Tudor Succession, which was potentially a gift for Walsingham