From the publisher:
This supplement details the d20 Modern Ninja prestige class that appears in the 1948 Campaign World. It also features the Cloak Dance feat, a description of a Japanese secret society (the Black Dragons), and one new talent for Fast heroes, providing everything you need to play a Ninja with the d20 Modern system. It also introduces Dragonfly, a 12th level Ninja NPC from the 1948 Campaign World. Her history, personality, and combat tactics are included along with a detailed stat-block.
The Ninja is a classic, archetypical character, suited for any d20 Modern campaign. If you are playing a 1948 campaign, however, this version of the Ninja is an essential element.
The legendary Ninjas of Japan are professional assassins, saboteurs and terrorists. They are also are students of philosophy, worshipers of ancient religion, and practitioners of dark arts. Many of them work for the imperil government as a 5th column of secret agents who infiltrate foreign countries before the Japanese army invades. They sometimes serve as spies or work to spread disinformation and fear among the enemy. They also terrorize civilian leaders in Japan, intimidating them into subservience to the Japanese military.
Ninjas are masters of stealth and combat. They also cast a limited number of divine spells, practice the secret martial arts style of ninjutsu, and are often associated with underground organizations such as the League of Blood or the Black Dragons.