This is the biography of the famous Irish detective and security policeman, John Mallon (1839-1915). Son of a small Catholic farmer in republican south Armagh, Mallon rose to be assistant commissioner of the Dublin Metropolitan Police and for 30 years used the G men (the Detective Division) to subvert revolutionary activity in Dublin. He was remarkably successful; his greatest triumph was bringing to the gallows the Invincibles, who had carried out the Phoenix Park murders. Mallon became a legend in Dublin, mentioned in Joyce’s Ulysses , very popular with his detectives, always courteous, never resorting to violence in dealing with suspects and a master of interrogation who personally controlled an army of paid informers - the Lord Lieutenant once remarking, ‘Without Mallon, we would have no one worth a row of beans’.