As a consequence of this drastic measure, the three leaders of the Opposition in the Legislature--Joseph Willcocks, Benjamin Mallory and Abraham Markle--who had been chiefly instrumental up to this time in thwarting all Brock's efforts, immediately fled to the United States, with which they had long been in traitorous intercourse, and where all their sympathies lay, Willcocks being eventually killed at the battle of Fort Erie, in 1814, in command of an American regiment, and Mallory serving throughout the war as a major in the same corps. This measure enabled Brock also to deal summarily with their disloyal partisans and followers, much more numerous and infinitely more dangerous than is now generally supposed. He immediately issued a proclamation ordering all persons suspected of conniving with the enemy to be apprehended, and treated according to law. Those who had not taken the oath of allegiance were ordered to do so or leave the Province; many were sent out of the country; large numbers left of their own accord; those who refused to take the oath or to take up arms to defend the country, and remained in the Province after a given date, were declared to be enemies and spies, and were treated accordingly; a large number of this disloyal element were arrested and imprisoned early in the war, as on the day of the Battle of Queenston Heights the jail and Court House at Niagara as well as the blockhouse at Fort George were filled with political prisoners, over three hundred aliens and traitors being in custody, some of whom were tried and sentenced to death, while others were sent to Quebec for imprisonment. This pressing and important business having been accomplished, General Brock entered actively upon his campaign, and determined upon offensive measures by an assault upon Detroit. Colonel Macdonell accompanied him as his military secretary and aide-de-camp. When the American, General Hull, in command of a greatly superior force and in possession of a strongly fortified position, on the 16th August proposed a cessation of hostilities with a view to his surrender, it was Colonel Macdonell whom General Brock entrusted with the delicate and important task of preparing the terms of capitulation. He returned within an hour with the conditions, which were immediately confirmed by General Brock, whereby Fort Detroit with 59,700 square miles of American territory--the whole State of Michigan--was surrendered. 2,500 officers and men became prisoners of war, and 2,500 stand of arms, thirty-three pieces of cannon, the _Adams_ brig-of-war, and stores and munitions of war to the value of L40,000, all so sorely needed by the Canadian militia, were handed over to the British Commander.