At this juncture Sir William Parsons and Sir John Borlase were at the head of the English Government in Ireland; they were in the interest of the Parliament, and were detested by almost all classes of Irish. Sir John Clotworthy, in the House of Commons, had openly declared that "the conversion of the Papists in Ireland was only to be effected by the Bible in one hand, and the sword in the other." Pym was reported to have said that they would not leave a priest in Ireland; and at a public entertainment Parsons had echoed those sentiments by declaring that "in a twelvemonth not a Catholic would be left in that country." The Irish were, therefore, delighted with their success with the king, and Gormanstown and his associates hastened home again, with two Bills signed by the king, granting the possession of lands which had been held sixty years, and setting aside all the sequestrations made by Strafford. But Parsons and Borlase, aware that the passing of these Bills would attach Ireland to the interests of the king, defeated the object by proroguing Parliament a few days before the arrival of the deputies.
It was now resolved by Ormond and Antrim to defer any movement till the reassembling of the Irish Parliament in November, when they could at the same moment secure Dublin castle and the persons of Parsons and Borlase, and issue in the name of the two Houses his Majesty's concession to the people of Ireland. But the native Irish, stimulated by the addresses of Moore, could not wait so long. They determined to rise, without waiting for the combined force, on the 23rd of October. Two hundred and twenty men were to surprise the castle, but at the time appointed only eighty appeared. They concluded to wait till the next day for the arrival of the rest, but that night one Hugh M'Mahon, in a drunken fit, betrayed the secret to Owen O'Connelly, a servant of Sir John Clotworthy, and a Protestant. He instantly carried the news to Sir William Parsons; the city gates were closed, and a quick search was made for the conspirators. All but M'Mahon and Lord Maguire escaped, but the castle was saved.
Ignorant of the failure of the plot, the people of Ulster rose on the appointed day. Charlemont and Dungannon were surprised by Sir Phelim O'Neil, Mountjoy by O'Quin, Tanderagee by O'Hanlan, and Newry by Macginnis. In little more than a week all the open country in Tyrone, Monaghan, Longford, Leitrim, Fermanagh, Cavan, Donegal, Derry, and part of Down, were in their hands. The other colonies in which there were English or Scottish plantations followed their example, and the greater part of Ireland was in a dreadful state of anarchy and terror. The Protestant people on the plantations fell beneath the butchering revenge of the insurgents, or fled wildly into the fortified towns. The horrors of the Irish massacre of 1641 have assumed a fearful place in history; the cruelties, expulsions, and oppressions of long years were repaid by the most infuriated cruelty. Men, women, and children, fell indiscriminately in the onslaught, and they who escaped, says Clarendon, "were robbed of all they had, to their very shirts, and so turned naked to endure the sharpness of the season, and by that means, and for want of relief, many thousands of them perished by hunger and cold."