Mitchel was a desperate fanatic, and had entertained a resolution of assassinating Sharpe, archbishop of St. Andrews, who, by his former apostasy and subsequent rigour, had rendered himself extremely odious to the covenanters. In the year 1668, Mitchel fired a pistol at the primate, as he was sitting in his coach; but the bishop of Orkney, stepping into the coach, happened to stretch out his arm, which intercepted the ball, and was much shattered by it. This happened in the principal street of the city; but so generally was the archbishop hated, that the assassin was allowed peaceably to walk off; and having turned a street or two, and thrown off a wig, which disguised him, he immediately appeared in public, and remained altogether unsuspected. Some years after, Sharpe remarked one, who seemed to eye him very eagerly; and being still anxious, lest an attempt of assassination should be renewed, he ordered the man to be seized and examined. Two loaded pistols were found upon him; and as he was now concluded to be the author of the former attempt, Sharpe promised, that, if he would confess his guilt, he should be dismissed without any punishment. Mitchel (for the conjecture was just), was so credulous as to believe him; but was immediately produced before the council by the faithless primate. The council, having no proof against him, but hoping to involve the whole body of covenanters in this odious crime, solemnly renewed the promise of pardon, if he would make a full discovery; and it was a great disappointment to them, when they found, upon his confession, that only one person, who was now dead, had been acquainted with his bloody purpose. Mitchel was then carried before a court of judicature, and required to renew his confession; but being apprehensive, lest, tho' a pardon for life had been promised him, other corporal punishment might still be inflicted, he refused compliance; and was sent back to prison. He was next examined before the council, under pretence of his being concerned in the insurrection at Pentland; and though no proof appeared against him, he was put to the question, and, contrary to the most obvious principles of equity, was urged to accuse himself. He endured the torture with singular resolution, and continued obstinate in the denial of a crime, of which, it is believed, he really was not guilty. Instead of obtaining his liberty, he was sent to the Bass, a very high rock, surrounded by the sea; at this time converted into a state prison, and full of the unhappy covenanters. He there remained in great misery, loaded with irons; till the year 1677, when it was resolved by some new examples to strike a fresh terror into the persecuted, but still obstinate enthusiasts. Mitchel was then brought before a court of judicature, and put upon his trial, for an attempt to assassinate an archbishop and a privy counsellor. His former confession was pleaded against him, and was proved by the testimony of the duke of Lauderdale, lord commissioner, lord Hatton his brother, the earl of Rothes, and the primate himself. Mitchel, besides maintaining that the privy counsel was no court of judicature, and that a confession before them was not judicial, asserted, that he had been engaged to make that confession by a solemn promise of pardon. The four privy counsellors denied upon oath, that any such promise had ever been given. The prisoner then desired, that the council books might be produced in court; and even offered a copy of that day's proceedings to be read; but the privy counsellors maintained, that, after they had made oath, no farther proof could be admitted, and that the books of council contained the king's secrets, which were on no account to be divulged. They were not probably aware, when they swore, that the clerk having engrossed the promise of pardon in the narrative of Mitchel's confession, the whole minute had been signed by the chancellor, and that the proofs of their perjury were by that means committed to record. Though the prisoner was condemned, Lauderdale was still inclined to pardon him; but the unrelenting primate rigorously insisted upon his execution, and said, that, if assassins remained unpunished, his life must be exposed to perpetual danger. Mitchel was accordingly executed at Edinburgh in January 1678. Such a complication of cruelty and treachery shews the character of those ministers, to whom the king had, at this time, entrusted the government of Scotland.