He probably intentionally failed to obtain a passport for Babington, and instead persuaded him that he, Poley, was a Catholic sympathiser and could be trusted. It was Babington's misplaced trust of, and possibly even love for, Poley that was a large contributory factor in his eventual downfall. During Elizabeth's reign her court was particularly concerned about the prospect of Mary Stuart coming to the throne. It was a time of great religious tension. The St. Bartholomew's Day Massacre served to increase the realisation of the outcome a return to Roman Catholicism might present. The Queen's security forces, led by Sir Francis Walsingham with its ruthless and cunning spies like Poley were more than effective at their job. During one of Walsingham's investigations, a suspected subversive named Gilbert Gifford was arrested and interrogated. To avoid punishment, Gifford agreed to act as a double agent. He made contact with the French Embassy in London and arranged the smuggling of letters from Mary Stuart to her followers. This was to be achieved through the use of beer barrels. Gifford ensured that Walsingham was given access to these communications which revealed Mary's requests to the French and Spanish that they intervene on her behalf. On 6 July 1586 Babington wrote to Mary Stuart, telling her that he and a group of friends were planning to assassinate Elizabeth, whom she (the Queen of Scots) would succeed. Babington's (and Mary Stuart's) defenders claim that in the sixteenth century it was held that the killing of "tyrants" was morally acceptable. Babington decided to write to Mary to seek her authorisation, which he believed she could provide as the legitimate claimant to the Throne. (It was believed by Catholics that Elizabeth's claim to the throne was void due to her being the daughter of Anne Boleyn whose marriage to Henry VIII they considered illegal due to Henry VIII's divorce from his first wife, Catherine of Aragon.) Mary replied to Babington, in which she stressed the necessity of foreign aid if the rescue attempt was to succeed. However, she left the matter of the assassination to Babington's conscience. In the meantime Babington's growing involvement with the plot was being reported to Walsingham, by Poley, who was by this time much in Babington's confidence, despite having been caught by him copying some of Mary's letters. When Walsingham and his officials had gathered sufficient evidence Babington and his crew were rounded