The bombing grew from a chain of events that had turned increasingly violent. The IRB, founded on St Patrick's Day 1858 with the aim of establishing an Irish republic, had an estimated 100,000 members by 1865. In September 1867, an attempt to free two Fenian leaders from a police van in Manchester resulted in the shooting death of Police Sergeant Charles Brett. Three of the five men arrested for the killing were hanged at Salford Gaol on 23 November, becoming the 'Manchester Martyrs' in the Irish nationalist memory. Three days before their execution, Burke was arrested in Woburn Square, London, and charged with treason. His imprisonment at the Middlesex House of Detention -- Clerkenwell Prison -- set the stage for the rescue attempt that would go catastrophically wrong.

The first attempt to blow through the prison wall, on 12 December, failed when the bomb did not explode. The plotters returned the next day. This time the detonation was devastating, but its victims were not the intended targets. The blast struck outward into Corporation Lane, a street of tenement houses where working-class families lived in close quarters. Twelve people died, all of them civilians who had nothing to do with the Fenian cause or the British state that was its enemy. The wounded numbered in the dozens at minimum, with estimates ranging above 120. The prison wall was breached, but the yard behind it was empty. Burke remained in his cell.

Eight people were charged, but two turned Queen's evidence. At trial at the Old Bailey in April 1868, Michael Barrett, a County Fermanagh man, was convicted of murder despite claiming he had been in Scotland on the day of the bombing. Some witnesses supported his alibi; one placed him at the scene. Barrett was hanged by William Calcraft outside Newgate Prison on 26 May 1868. He was the last person to be publicly hanged in England. Three days later, the Capital Punishment Amendment Act ended the practice of public execution. Burke himself was convicted of treason and sentenced to fifteen years of penal servitude. Queen Victoria, reportedly frustrated that only one man was convicted, wrote to the Home Secretary expressing a wish that perpetrators of such crimes 'be lynch-lawed on the spot.'

The bombing's immediate effect was to enrage the British public and undermine sympathy for the Irish cause. Karl Marx, living in London, warned that English workers would be 'driven into the arms of a reactionary government.' Punch magazine published a cartoon of the 'Fenian Guy Fawkes' surrounded by innocent women and children. Prime Minister Disraeli pushed for the suspension of habeas corpus, and thousands of special constables were recruited. The Metropolitan Police created the Special Irish Branch at Scotland Yard in 1883 to monitor Fenian activity -- the ancestor of today's Special Branch. Yet the explosion also had a less predictable consequence. William Gladstone, then in opposition, announced within days that Irish grievances must be addressed. He later credited the Clerkenwell explosion with turning his mind toward Home Rule. When Queen Victoria asked him to form a government, he declared: 'My mission is to pacify Ireland.' The supreme council of the IRB itself condemned the bombing as a 'dreadful and deplorable event.' Even Charles Stewart Parnell acknowledged the paradox, noting that 'no amount of eloquence could achieve what the fear of an impending insurrection' had achieved. The prison was demolished in 1890. A plaque on the Hugh Myddleton School, which now occupies the site, commemorates the twelve people who died in an act of political violence that failed on its own terms yet reshaped the political landscape of two nations.