The movie begins with a group of police officers pursuing a rogue ninja, who is rampaging through a golf course. The ninja is eventually killed by the police, but his spirit possesses a young female aerobics instructor named Christie (played by Lucinda Dickey).
After Christie witnesses the ninja's death, she discovers his sword and takes it home with her. That night, she is attacked by the ninja's spirit and is brought under his control. The spirit seeks revenge against the people who killed him, and Christie begins carrying out his mission.
As Christie continues to be possessed by the ninja's spirit, she begins to have disturbing visions and violent outbursts. She also meets a handsome, mysterious stranger named Yamada (played by Sho Kosugi), who reveals that he is a ninja and offers to help her.
Together, Christie and Yamada track down the people responsible for the ninja's death. Along the way, they must face off against the supernatural powers of the possessed aerobics instructor, as well as a team of evil ninjas who are trying to stop them.
The movie features plenty of action-packed fight scenes, as well as some impressive special effects for its time. It also includes a memorable training montage in which Christie learns how to be a ninja from Yamada.
In the end, Christie is able to overcome the evil spirit and regain control of her body. With the help of Yamada, she is able to defeat the remaining ninjas and bring the ninja's spirit to rest. The movie ends with Christie and Yamada sharing a romantic moment, as she reflects on the strange and dangerous journey they have been through together.