From the publisher's website:
The very archetype of the mystic spy or assassin: A shadowy figure as much a master of the dark arts as an outlaw. From the Hashsh’shin to the Sicarii, the black-clad assassin clans of Japanese lore to the fanciful depictions of Wuxia films, the ninja is an icon of fantasy and pop culture—ironic, for a creature that lives by secrecy and a mastery of deception and disguise.
Ultimate Options: Power of the Ninja presents 50 new tricks and master tricks for the ninja, along with 8 new ninja-related feats and four variant ninja classes, and is 20 pages long! With this broad set of new resources you can expand the role of ninja-style assassins in your campaign, or leave behind the Asian-themed trappings to integrate the stealthy, deceptive mystic spy concept in a manner that best suits your campaign setting.
The Ultimate Options series of products focuses on topics introduced in the Ultimate Magic book for Pathfinder, expanding options for players using that book.