This he showed no signs of doing, but merely desired a number of the leading covenanters to appear before him. Six only obeyed, at the risk, some thought, of imprisonment or death, but neither Rothes nor Montrose, who headed them, was given to think of peril to themselves.
The old covenanter seems to have told Charles some plain truths, and the king in return forgot the courtesy which so distinguished him, and retorted that Rothes was a liar. No man was present when Montrose was summoned to confer with the king, and neither he nor Charles ever let fall a word upon the subject; but after that day his friends noted that he was no longer as bitter as before against his sovereign, nor so entirely convinced that the covenanters were right in their acts. Yet, whatever his feelings may have been, he strongly opposed the king's desire of filling the bishops' vacant places with inferior clergy at the meeting of Parliament, and, as might have been expected, the assembly was prorogued, leaving matters precisely as they were.
After this the Scotch took on themselves the management of their own affairs, and a Committee of Estates was formed, to which was entrusted absolute power both in state and army. Leslie was one of this committee; Montrose was another, and immediately he set about raising troops from his own lands, and carried out the plan of campaign that had been agreed on by attacking Airlie castle. On its surrender he garrisoned it with a few men, and went away; but shortly after Argyll arrived, turned out the garrison, and burned the castle, at the same time accusing Montrose of treason to the covenant in having spared it. But the Committee of Estates declared Montrose 'to have done his duty as a true soldier of the covenant,' and the accusation fell to the ground.
Montrose, however, though entirely cleared of the charge, was not slow to read the signs of the times. He saw that the covenanters were no longer content with guarding their own liberties of church and state, but desired to set at naught the king's authority, perhaps even to depose him. So he and certain of his friends, Mar, Almond, and Erskine among them, formed a bond by which they swore to uphold the old covenant which they had signed in 1638, 'to the hazard of their lives, fortunes, and estates, against the particular perhaps indirect practising of a few.' This was the covenant to which Montrose held all his life, and for which he was hanged beside the city cross.
Having as he hoped taken measures to checkmate Argyll, Montrose joined the army, which had now swelled to twenty-five thousand men, was the first to cross the Tweed at Coldstream, and marched straight on Newcastle. The town surrendered without firing a shot, and Montrose sent a letter to the king again professing his loyalty. When later he was imprisoned on a charge of treason to the covenant in so doing, he answered that his conscience was clear in the matter, and that it was no more than they had all declared in the covenant, which no man could deny. But soon another storm was raised on account of the famous bond which he and his friends had made a short time before they were put in prison, and the clamour was so great that even his own party was alarmed, and gave it up to be burned by the hangman.
Montrose's next object was to induce the king to come to Edinburgh in order to persuade the Scotch that he was ready to keep his word, and to grant the country the religious and civil liberties demanded by the covenant. Charles came, and was gracious and charming as he knew how to be, even going to the Presbyterian service, which he hated. This pleased everyone, and hopes ran high; but the quarrel was too grave to be soothed by a few soft words spoken or a few titles given. Plots and rumours of plots were rife in Edinburgh, and the king was forced to employ not the men he wished, but the men whom the Parliament desired. In November he returned to England, first promising that he would never take into his service Montrose, who had just been released after five months spent in prison, where he had been thrown with the rest of his party after the discovery of the bond.
To one who knew Scotland as well as he it was apparent that the Scotch Parliament and the English would speedily join hands, and he retired to one of his houses to watch the course of events. The covenanters tried to win him back, but Montrose felt that they disagreed among themselves, and that it would be impossible for him to serve under them. Meanwhile in England things marched rapidly: Edgehill had been fought; episcopacy had been abolished by Parliament in England as well as Scotland; and Hamilton's brother Lanark was using the Great Seal to raise a Scotch army against the king, for, by a treaty called the Solemn League and Covenant, Scotland was to fight with the English Parliament against the king, and England was to abolish bishops and become presbyterian like Scotland. England, however, did not keep her promise.