Whilst Sinclair was thus undermining the welfare of the party to which he nominally belonged, his determined enemy, Sir John Schaw, after assisting the Duke of Argyle in defending Inverness against the insurgent troops, was marching with Lord Isla to rejoin the Duke of Argyle in his march towards Perth. It so happened that Lord Isla and his friends reached Sherriff Muir at the very moment when the Government troops and the Jacobites were about to join in battle. "Sir John," says Sir Walter Scott, "though he had no command, engaged as a volunteer; and we may suppose his zeal for King George was heightened by the recollection that the slayer of his brothers fought under the opposite banners." He behaved himself with distinguished courage, receiving a wound on his arm, and another in his side.[235] He was, at this time, the only surviving brother out of four, his brother Thomas having been slain at the siege of Mons a year after the death of the others. A month before Sir John Schaw had joined the Duke, Lady Schaw, the daughter of Sir Hugh Dalrymple, and a woman of singular energy and spirit, assembled the Greenock companies in arms, and telling them that the Protestant religion, with their laws, liberties, and lives, and all that was dear to them as men and Christians, were in hazard by that unnatural rebellion, exhorted them to conduct themselves suitably to the occasion. The conduct of Sinclair at the battle of Sherriff Muir was not inconsistent with his former life. He remained, in that engagement, stationary, with the Marquis of Huntley, at the head of the cavalry of Fife and Aberdeen; hence the lines in the old song on Sherriff Muir. "Huntly and Sinclair They baith play'd the Tinkler, With consciences black as a craw, man." Upon the return of the Jacobite army to Perth, where they waited, as Scott remarks in a tone of mournful reprobation of Mar, "until their own forces should disperse, those of their enemy advance, and the wintry storm so far subside as to permit the Duke of Argyle to advance against them," Sinclair was the chief promoter of a scheme formed by the Grumblers for a timely submission to Government. Instigated by their wishes, an attempt was made by Lord Mar to procure, through the Duke of Argyle's mediation, some terms with Government; but it failed, and those who had embarked in the cause were obliged to provide, as they best might, individually for their safety. The whole tenour of Sinclair's conduct was such as to draw down upon him the severest invectives of his party. In one of the poems of the day he is thus described: "The master with the bully's face, And with the coward heart, Who never fail'd, to his disgrace, To act a coward's part, Did join Dunbogue, the greatest rogue, In all the shire of Fife, Who was the first the cause to leave, By counsel from his wife."