For every day of her long reign, Elizabeth's advisors worried that she might be assassinated by Catholics viewing her as an illegitimate Queen. An entire network of spies, working to insure Her Majesty's safety, made sure that plots were uncovered and would-be perpetrators executed.
At first, William Cecil (later known as Lord Burghley) assessed whatever intelligence came to light. But after Mary Queen of Scots crossed the border into England, Elizabeth's advisors were alarmed. With her own claim to the British throne, the Queen's cousin would likely be a magnet for every Catholic conspiracy which could be imagined. Looking for someone he could trust to serve as spy master, Cecil turned to Sir Francis Walsingham, a staunch Protestant.
Since 1568, Walsingham had served as Elizabeth's Secretary of State. From spies which he sent to other countries, he could assess attitudes toward Britain's Queen. From intelligence-gatherers in England, he could judge the pulse of the people toward their monarch.
Knowing conspirators communicate by code, Sir Francis arranged for his spies to be schooled in their ways. If a plot were in the works, Elizabeth's protectors needed to unravel it.
As time went on, Mary Queen of Scots increasingly pressed to go home. There was always a reason why her English captors would not let her go. The main, unstated reason was clear. Elizabeth and her advisors continued to view Mary - the heir - as a threat to the security of Her Majesty's throne. Walsingham allowed Mary to be moved - from place to place to place - but only inside Britain.
Elizabeth's men were not alone in thinking about Mary. Many ardent Catholics still thought that she - now quite ill with various ailments, including rheumatism - should be queen of both Scotland and England.
Walsingham decided to concoct a scheme that would implicate Mary once and for all.
Using Sir Anthony Babington (an unsuspecting Catholic) as his pawn, Sir Francis allowed Mary to secretly correspond with Babington (who wanted to help Mary escape). Mary's two secretaries coded all messages, but Walsingham knew the cipher. Anxious to be free, and relieved someone was finally talking about escape, Mary responded to Babington's letters.
If the letters had just talked about escape, Walsingham's efforts would have come to nothing. But in one letter Babington went much farther than the subject of escape. He could not resist a reference to Elizabeth. Babington wanted to know if Mary would reward him and his compatriots "For the dispatch of the usurper." (Follow this link to read Babington's letter.) Once again ignoring the advice of her counselors, who were concerned about the veiled reference to a plot against Queen Elizabeth, Mary wrote to Babington.
While she said nothing at all about Elizabeth, Mary did agree to Babington's proposed plans for her escape. Her signature was on the letter. Someone else forged a postscript, asking for information about the conspirators. Babington dutifully responded, thereby insuring the ultimate deaths of himself and his colleagues.