Colonel Kelly and another man come to Manchester "to free old Ireland from her tyrant's chain." They are jailed. Allen, Larkin and O'Brien stage a rescue. They are taken, found guilty, and hanged.
OLochlainn-More: "The Manchester Martyrs were Allen, Larkin and O'Brien, all three hanged in revenge for the accidental shooting of Constable Brett in the attempted rescue of Kelly and Deasy, two Fenian Leaders in 1867." - BS
We should probably note that Kelly and Deasy, while in British custody, were not really in danger of execution. Thomas J. Kelly, who had been proclaimed chief executive of the Fenian's Irish Republic, and one Captain Timothy Deasy were simply being transported from court to prison, but they were "rescued" anyway on September 18.
In the course of the "rescue," a police sergeant, Charles Brett, was killed. William Allen, Michael Larkin, and Michael O'Brien were convicted of the murder and executed on November 23. The three men came to be known as the "Manchester Martyrs." A later rescue attempt also failed, but managed to kill a dozen bystanders.
Nonetheless, both sides blamed the other, increasing Anglo-Irish tensions. The incident also increased rebel recruiting, despite the fact that the Irish had committed the initial crime and the fact that the British followed the law throughout.
For additional background, see the notes to "The Smashing of the Van (I)." - RBW