Knox's final encounter with Mary was prompted by an incident at Holyrood. While Mary was absent from Edinburgh on her summer progress in 1563, a crowd forced its way into her private chapel as Mass was being celebrated. During the altercation, the priest's life was threatened. As a result, two of the ringleaders, burgesses of Edinburgh, were scheduled for trial on 24 October 1563. In order to defend these men, Knox sent out letters calling the nobles to convene. Mary obtained one of these letters and asked her advisors if this was not a treasonable act. Stewart and Maitland, wanting to keep good relations with both the Kirk and the Queen, asked Knox to admit he was wrong and to settle the matter quietly. Knox refused and he defended himself in front of Mary and the Privy Council. He argued that he had called a legal, not an illegal, assembly as part of his duties as a minister of the Kirk. After he left, the councillors voted not to charge him with treason.