In December 1585, Gilbert Clifford was arrested in Sussex. While being interviewed, Clifford confessed that he had been involved in a Catholic plot to overthrow Elizabeth I. The man in charge of protecting Elizabeth was Francis Walsingham. He offered to release Clifford if he was willing to work as a double-agent. Clifford agreed and went to his contact in the French embassy telling him that he knew how to smuggle letters to and from Mary Stuart. He explained that every week a barrel of beer was sent from Burton to where Mary was imprisoned. Clifford arranged to have letters placed in a waterproof package inside the stopper of the barrel.
Another double-agent, Thomas Philips, who was inside the prison, told Mary how she would be receiving letters in her beer barrel. However, before they were placed inside the beer barrel, they were read by Walsingham. More importantly, Francis Walsingham was also able to read the letters that Mary sent to her Catholic friends in France and Spain. In these letters Mary explained how she wanted France and Spain to help her become queen by invading England.
Walsingham allowed the letters to continue to be sent because he wanted to discover who else was involved in this plot to overthrow Elizabeth. Eventually, on 25 June 1586, Mary wrote a letter to Anthony Babington. In his reply, Babington told Mary that he and a group of six friends were planning to murder Elizabeth.
Walsingham was now ready to act. Babington was arrested and his home was searched for documents that would provide evidence against him. When interviewed, Babington made a confession in which he admitted that Mary had written a letter supporting the plot.
Anthony Babington and six others were executed for high treason on 18 September, 1586. An attempt to kill the monarch was the most serious crime in England and the punishment was to be hung, drawn and quartered. The men were tied face downwards on a hurdle drawn by horses. They were then dragged through the streets of London. At Tyburn they were hung for a short period. After being revived the men had their intestines cut out.
At the execution the crowd complained about the agonies the men had to suffer before they died. When she heard this Elizabeth gave instructions that the rest of the conspirators due to be executed the next day should be dead before they were cut down.
Elizabeth was also against Mary Stuart being executed for her part in the plot, and for six weeks refused to sign her death warrant. Walsingham and Parliament insisted that Mary should die. On 8 February, 1587 Mary was beheaded. Afterwards, Elizabeth claimed that she had not given permission for Mary to be executed. As a result, Davidson, the man responsible for the execution, was fined £6,000 and imprisoned in the Tower of London.