But if Cromwell was disposed to allow Ormond to escape, he was compelled to make an example of some other of the Royalist agitators. On the 12th of March the Protector sent for the Lord Mayor and aldermen to Whitehall, informed them that the Duke of Ormond had been lurking in the City to excite rebellion, and that it was necessary to take strict measures for putting down the seditious of all sorts. At the same time he ordered the fleet to sweep the coasts of the Netherlands, which drove in there two fleets intended for the Royalist expedition, and blockaded Ostend. He then determined to bring to justice some of the most incorrigible agitators. Sir Henry Slingsby, who had been confined in Hull ever since the outbreak of Penruddock, had not even there ceased his active resistance, employing himself to corrupt the officers of the garrison, who, being instructed by the governor, appeared to listen to his views, so that ere long he was emboldened to offer them commissions from Charles Stuart. Another person arrested was Dr. Hewit, an Episcopalian clergyman, who preached at St. Gregory's, near St. Paul's, and was a most indefatigable advocate of a royal invasion. There were numbers of the Royalist apprentices and others in the City, who were not patient enough to wait for the invasion; they resolved to rise on the 15th of May, fire the houses near the Tower, and by sound of drum proclaim the king. The Protector told Thurloe that "it was not fit that there should be a plot of this kind every winter," and Thurloe had made himself thoroughly aware of all their proceedings. As the time approached, the ringleaders were seized at the "Mermaid," in Cheapside. A High Court of Justice was appointed according to Act of Parliament, and Slingsby, Hewit, and the City incendiaries were tried. There was ample proof of their guilt. Hewit denied the authority of the court and refused to plead, but he was all the same condemned with Slingsby and six of the City traitors to death.