The Iga region of feudal Japan, a mountainous pocket largely outside the control of the great samurai clans, produced the warriors history remembers as ninja. This film traces how geography and politics let Iga and neighboring Koga develop their own military culture, training operatives in espionage, sabotage, and assassination rather than open battle. It follows the region's eventual collision with Oda Nobunaga, whose forces invaded Iga in a campaign that nearly wiped out the ninja clans, and examines how surviving practitioners were absorbed into the military and intelligence networks of later warlords and the Tokugawa shogunate. Historians and re-created training sequences separate the documented reality, poison, disguise, reconnaissance, coded messages, from the later myth-making that turned ninja into superhuman assassins in popular culture. The result is a grounded account of how a marginal mountain society turned irregular warfare into a specialty valuable enough that Japan's rulers kept hiring it, long after the age of the samurai had otherwise closed ranks around conventional armies.