A letter dated May, 1558, sent from Rome and directed to O'Neal, sent many Protestants to their death and others in a big hurry to leave the Island. Not long after Mr. O'Neal received this letter he had Thaddy O'Brian, an Irish bishop of Cashel, made a prisoner. He was a direct descendant of Morgan O'Brian, who was the son of King Brian. After examination and search was made, Thaddy O'Brian was pilloried and mistreated in every, way until the king's orders arrived in what manner he should further be disposed of. But orders came from England that he was to be hanged. Rough men laid violent hands on him in his castle in Dublin, and drug him forth to a scaffold at Gallowsgreen where, after being hanged, he hung for some time before burial.

Not long after the death of Thaddy a plot was hatched by the papists for the destruction of the Protestants; and it failed not of the success wished by its malicious and rancorous projectors. The design of this horrid conspiracy was that a general insurrection should take place at the same time throughout the kingdom, and that all Protestants, without exception, should be murdered. The day fixed for the horrid massacre was the twenty-third day of October 1641, the feast of Ignatius Loyola, founder of the Jesuits; and the chief conspirators in the principal parts of the kingdom made the necessary preparations for the intended conflict. The plot was discovered by Owen O'Connelly. Owen had married Helen Brian, daughter of Thurmond Brian, of Dublin.

Even with the discovery of the plot, the bloody part of the intended tragedy was past prevention. The Catholics were in arms on the day appointed, and every Protestant who fell in their way was immediately murdered, no age, no sex, no condition was spared.