A Kunoichi, a female Ninja, has begun murdering Yakuza members in Tokyo. The murders are violent and nearly impossible to believe. Trace Conner, an American Ninjutsu instructor, is asked to come to Japan and help because it is believed that he knows the Kunoichi and may be able to stop her. Once there, Conner finds that he does know her but has almost no hope of stopping the murders. Following a trail of death that takes him all over Japan, he tries to catch the killer without getting killed himself. In the process, he learns aspects of Ninjutsu that had been hidden from him for more than a decade.