Elizabethan Spies and Plots: How Francis Walsingham Caught Ambassadors Plotting to Overthrow Queen Elizabeth I
- Feb 9
- 6 min read
Updated: Apr 1
Three Ambassadors. One Double Agent. And the Secret War for England’s Throne.
In mid-October 1583, Sir Francis Walsingham, Queen Elizabeth I’s spy-master, had a serious spy problem.
Actually—he had three, but he didn’t know that.
Walsingham was convinced that a hidden and coordinated Catholic plot was forming to kill one queen and crown another. He just didn't know who was leaking the information behind it. And without knowing who, he couldn't stop it.
The target was Elizabeth I. Her replacement would be her Catholic cousin.
Mary Stuart, Queen of Scots had fled Scotland years earlier, arriving in England as a supplicant. Elizabeth, wary and reluctant, had granted her protection. Under pressure from her Privy Council, Elizabeth had confined her cousin because wherever Mary went, factions gathered. If Mary escaped, especially back to France where she had once been queen, an invasion of England was not merely possible, but likely.
Yet for all his spies, intercepted letters, and cipher-breaking skill, Walsingham could not see the full shape of the conspiracy. He did not yet know who was coordinating it, how it would unfold, or where to strike.
The uncertainty made him twitchy.
A lone-wolf attempt on Elizabeth’s life by one John Somerville earlier that summer had rattled nerves across court and council. In a world where spies watched spies, and every report might itself be a lie, even Walsingham, known to all as “Mr. Secretary”, was groping in the dark.
Then, pure chance lit the path for him.
Unbidden, an anonymous source inside the French ambassador’s household began sending Walsingham a stream of astonishing intelligence.
One letter contained this quiet bombshell:
“I have made the ambassador’s secretary so much my friend that, for some little reward, there is nothing he will not let me know—especially all that touches the Scottish Queen and the secret writing in which her letters are written.
After your excellency has inspected any packet addressed to her, he can insert others without anyone knowing at all.
The chief agents of the Scottish Queen are Mr. Throckmorton and Lord Henry Howard. They never come here except at night.”
More about the particularly villainous Lord Henry Howard (both in real life and in my novels) will be revealed later, but for now, think about how much intelligence that bombshell revealed. Someone inside the French ambassador’s household could:
🕵🏻♂️ Give Walsingham secret information about Mary Queen of Scots’ coded letters
🕵🏻♂️ Slip false information into packets going to her
🕵🏻♂️ Named two English traitors and spies.
Even more remarkable, this unsolicited information led straight to two other men, that very moment charmingly bowing and smiling at Elizabeth’s court: the Spanish ambassador and the French ambassador. They were both quietly, persistently working to put Mary Stuart on England’s throne.
Walsingham now faced an ambassadorial problem. Actually, three very different ones.
🇪🇸 The Spanish Ambassadorial Plot: Don Bernardino de Mendoza
The most obvious threat was the Spanish ambassador, Don Bernardino de Mendoza.
Mendoza had been meeting twice weekly in London with Nicholas Throckmorton, a key English Catholic agent just named by the anonymous source. Together, they planned to land 20,000 Spanish troops in England’s Catholic north, with the backing of King Philip II of Spain. From there, Elizabeth would be deposed. Mary would reign.
When Throckmorton was arrested, a small green velvet casket stuffed with ciphered letters to Mary from Paris was hidden beneath his bed. In a moment of desperate cunning, it was smuggled out of the house during the search and delivered straight to Mendoza.
Under questioning, Throckmorton denied everything. Then he broke.
He confessed that he and his brother had surveyed English landing sites for invading forces led by the Duke of Guise, and chosen Arundel, in Sussex.
On January 19, 1584, Mendoza was summoned to the Lord Chancellor’s house.
Seventeen Privy Councilors may have been present, but only three of them ever mattered: Walsingham, William Cecil, Lord Burghley, 🔗 William Cecil, Lord Burghley: Elizabeth's most calculating political survivor, and, Elizabeth’s favorite bad boy, Robert Dudley, Earl of Leicester, 🔗Robert Dudley, Earl of Leicester: Elizabeth's most dangerous favorite.
When those three escorted you into a private chamber, you knew the game was up.
Walsingham laid out the offenses with surgical precision: the meetings, the letters, the confessions, the proposed invasion. Mendoza was given fifteen days to leave England, or be removed by force.
Mendoza exploded.
“Elizabeth”, he thundered, “should stop stirring rebellion in other men’s realms before accusing innocent ambassadors of the same.”
Walsingham coolly replied that Mendoza was fortunate to escape with his life.
Storming out, Mendoza hurled one final flourish, “Don Bernardino de Mendoza was born not to disturb kingdoms—but to conquer them!”
He was expelled. England would not see another Spanish ambassador during Elizabeth’s reign.
🇫🇷 The French Ambassador and Mary Queen of Scots’ Secret Letters
The French ambassador, Michel de Castelnau, Sieur de la Mauvissière, was another matter entirely.
Mauvissière was no blunt instrument. He was experienced, subtle, and deeply entangled with Mary Stuart’s long cause. He had escorted her back to Scotland in 1560 after the death of her young French husband, King Francis II. He had spent years trying to reconcile Elizabeth and Mary. He had served in England through massacres, wars, and shifting alliances.
Unlike Mendoza, Mauvissière was not plotting troop landings.
He was doing something more elegant and just as dangerous.
He was acting as a reliable conduit for ciphered correspondence between Mary and her allies in France. Letters flowed quietly through his household. Plots matured in ink and code.
On paper, the solution seemed simple: expel him, too.
Elizabeth’s Privy Council even drafted the charges:
📜 Secret intelligence with the Scottish Queen
📜 Soundings of English Catholic loyalty
📜 Conveyance of treasonous letters
📜 Encouraging Elizabeth’s subjects toward Mary
And yet, Walsingham did nothing.
Why?
It might have been that Walsingham waivered over personal feelings. The French ambassador was an old friend who had escorted Walsingham from his Paris lodgings to the (relative) safety of the French court during the St. Bartholomew’s Day Massacre in Paris. 🔗 the St. Bartholomew's Day Massacre, when a single intercepted letter revealed a bloodbath.
But here, chance intervened. Hidden inside Mauvissière’s own household was Walsingham’s most precious asset of all.
🪆 An Elizabethan Secret Within an Elizabethan Secret
The anonymous informant had a name, or at least a borrowed one, not at all uncommon in the age of pseudonyms which was Elizabethan England.
He called himself Henry Fagot.
Fagot was a double agent embedded in the French ambassador’s service: trusted by Mauvissière, indispensable to Mary’s correspondence, and utterly loyal to Walsingham. So trusted was he that Mauvissière wrote to Mary assuring her that no one knew of their dealings except Fagot:
“He never budges from my chamber. He writes everything before me and in my presence. Thus neither the Queen of England nor her Council know anything.”
Except they did.
Through Fagot.
When Catholic agents in Paris began to suspect that Mauvissière himself was unreliable, Walsingham seized the moment. Quiet pressure was applied. Mauvissière was urged to cease communication with Mary and submit his letters for inspection.
Call it blackmail, or diplomacy, or what you will.
Within a year, Mauvissière was recalled to France. The channel closed. The Catholic plot withered.
🏴 England’s Own Ambassador Turns Traitor
But it would take several centuries for it to come to light that there was a third ambassador very much in the treasonous mix against England.
His identity was quite the Elizabethan Secret: Sir Edward Stafford, England’s own ambassador to France and husband to Leicester’s scorned lover and possibly legal wife, Douglass Sheffield. (That tangled romance is another Elizabethan Secret!)
Stafford became English ambassador to France in 1583, and began selling his services and confidential information to the former Spanish ambassador to England, now repurposed as Spanish ambassador to France, that self-declared conqueror, Bernardino di Mendoza. There wasn’t sufficient proof at the time, but it was very curious that Stafford sent multiple dispatches home to England portraying France as highly untrustworthy, and Spain and Philip II as a worthy ally for the ages.
⚖️ Weighing the Choices Between Secrets and Survival
In Elizabethan England, diplomacy, warfare, and espionage were not separate arts. They were threads of the same tapestry, pulled tightly, loosened, or cut by chance as much as by design.
And one anonymous spy, writing from inside a foreign ambassador’s chamber, altered the fate of a kingdom.
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