Wishart was burned in St. Andrews in March, 1546, and in May of the same year Cardinal Beaton was murdered. The cardinal's murderers held possession of the castle of St. Andrews; and, as Knox was known to be the enemy of Beaton (though he had no share in his assassination), he was forced (1547) for his own safety to join them with his pupils. Here his zeal and theological attainments made him so conspicuous that, at the instance of the leaders of the reforming party (Sir David Lyndsay among the rest), he was formally called to the ministry, and preached with much acceptance in the castle and parish church of St. Andrews. A few months later the castle surrendered to the French; and, in the teeth of the express terms of capitulation, the more prominent of the besieged party were sent as prisoners on board the French galleys. For eighteen months Knox remained a captive, his first winter being spent in a galley on the Loire, the second in prison in Rouen. His constitution was not naturally robust, and his hard experience during these two years seriously impaired his health for the rest of his life. The breach of faith on the part of the French, and the ignominy to which he was subjected, were never forgotten by Knox, and must in part explain and justify his life-long conviction that no good thing could come of French policy or French religion. In February, 1549, on the express intercession of Edward VI., Knox regained his liberty. As it was still unsafe for him to return to Scotland, for the next four years, till the death of Edward VI., he made his home in England. From all that is known of him during these years, it is clear that he made himself a person to be reckoned with by those at the centre of authority in the country. By his preaching at Berwick he gave such offence to the Bishop of Durham that he was removed to Newcastle, where it was supposed his influence would be less mischievous. In 1551 he was appointed one of six chaplains to Edward VI., and in 1552, at the suggestion of the Duke of Northumberland, he was offered the bishopric of Rochester. As the duke's object in suggesting the appointment was simply to check, as far as he could, what he deemed the dangerous activity of Knox, the offer was unhesitatingly rejected. Knox's importance in England is still further proved by the fact that, along with five others, he was consulted by Archbishop Cranmer regarding his forty-five (afterward forty-two) articles of religion.