What to read after Ninja, the Invisible Assassins?

Ninjutsu has been variously described as the "art of sneaking in," the "art of stealth" and even the "art of invisibility," and this book reveals the ninja's way of life that few outside of Japan have experienced. Ninja were the cloak-and-dagger artists of Japan's feudal era, from the late 13th century to the early 17th century. Japanese youths were trained within the Iga and Koga ninja networks, which were run like armed camps and turned out only espionage agents. Iga and Koga youths were born ninja and died ninja--there was no other way of life open to them. They were thus able to devote all their time to training, and they were considered full-fledged ninja when they were still in their teens.