At the height of the Irish Famine, now considered the greatest social disaster to strike nineteenth-century Europe, Anglo-Irish landlord Major Denis Mahon was assassinated as he drove his carriage through his property in County Roscommon. Mahon had already removed 3,000 of his 12,000 starving tenants by offering some passage to America aboard disease-ridden "coffin ships," giving others a pound or two to leave peaceably, and sending the sheriff to evict the rest. His murder sparked a sensation and drove many of the world's most powerful leaders, from the queen of England to the pope, to debate its meaning. Now, for the first time, award-winning journalist Peter Duffy tells the story of this assassination and its connection to the cataclysm that would forever change Ireland and America.