As one of the Protector’s retainers, he was probably involved in his plot to revolutionize the government. The gendarmerie upon the muster day were to be attacked by two thousand men under Sir Ralph Vane, and by a hundred horse of the Duke of Somerset’s, besides his friends, who were to stand by, and the idle people who, it was calculated, would take part. After this was done, the Protector intended to run through the city and proclaim, “Liberty! Liberty!” But the plot was discovered in time, and Somerset and his chief accomplices were committed to the Tower, 17 October, 1551. The Council gave orders for Stucley’s apprehension, but he escaped in time, and took refuge in France, where he devoted his sword to the service of Henry II, who entitled him “mon cher et bon ami.” He must have fought in the campaign of Henry against the Emperor Charles V in 1552, when Metz was taken by fraud. He was certainly received as a disaffected subject, and was admitted to the French counsels. In 1552 he returned to England with a story which he hoped would purchase his pardon. This was to the effect that Henry II meditated a sudden attack upon Calais. According to his account the French King himself had spoken to him of the weak points in the defences, had pointed out the very plan of assault by which, six years later, Calais was actually taken. Moreover, according to his scheme, the Scots were to enter Northumberland; Henry II would land troops at Falmouth, and the Duke of Guise would land at Dartmouth, which he knew to be undefended. Cecil suggested that Stucley should be sent back to France to acquire further information; but the Duke of Northumberland sent Stucley’s report to the French King, and committed Stucley to the Tower. Henry denied the truth of what had been reported. The payment of his debts, which had been promised to Stucley as a reward for his revelations, was now refused, and he remained in prison to the end of Edward’s reign. He was released on 6 August, 1553, but his debts compelled him again to leave England. Unable to return to France, he betook himself to the Emperor, and he was at Brussels in the winter of 1553-4, and served with the Imperial army at St. Omer. Philibert, Duke of Savoy, invited Stucley to accompany him to England in October of 1554, and Stucley accordingly appealed to Queen Mary for security against arrest whilst in her dominions, and this was granted to him for six months, and at the end of December he accompanied the Duke to England.