On May 17, 1980, on the eve of Peru's presidential election, five masked men stormed a small town in the Andean heartland. They set election ballots ablaze and vanished into the night, but not before planting a red hammer-and-sickle banner in the town square. The lone man arrested the next morning later swore allegiance to a group called Shining Path. The tale of how this ferocious group of guerrilla insurgents launched a decade-long reign of terror,...