During the morning rush hour of March 11, 2004, ten bombs exploded nearly simultaneously on Madrid’s commuter trains, killing 191 people and injuring almost 2,000. Reinares’ examination of that brutal attack may be the most thoroughly researched study of a European terrorist incident currently available to the public. Based on law enforcement records and media reports from a half-dozen countries, the book reconstructs the perpetrators’ background as petty criminals, their radicalization in prison, and the material benefits they gained from terrorism. They belonged to a sophisticated global network of al Qaeda–linked jihadists. Their ostensible motives ranged from simple retaliation for recent Spanish police crackdowns on a local al Qaeda cell to a surprisingly intense desire to exact revenge for the Christian conquest of Spain over five centuries ago. About a month after the attack, the seven main perpetrators detonated themselves to avoid police capture. But peripheral members of the conspiracy escaped to Iraq and eventually joined the Islamic State, or ISIS. The book closes by reminding readers that the transit systems in London, New York City, and other metropolitan areas remain at risk—and that the best way to combat the threat is to reinforce international coordination of intelligence and policing. This is a must-read for counterterrorism authorities and concerned citizens alike.