Casey Bowman is an American orphan, who is adopted into a martial arts
dojo in
Japan. Due to his perseverance and desire to master
bushido, Casey earns the respect of his
Sensei Takeda and his daughter Namiko. However, the dojo's top student Masazuka becomes bitter over Namiko's friendship with Casey. One morning, during a sparring match, Masazuka loses his temper and nearly kills Casey by throwing a
katana at him. In self-defense, Casey scars Masazuka below his right eye. As a result of his actions, Masazuka is expelled from the dojo by Sensei Takeda. Years later, Masazuka becomes an assassin of an organization called "Temple Industries", which itself runs an
underground cult known as "The Ring". He returns to his former dojo and claims the succession as
sōke, but Takeda turns him down. Anticipating an invasion by Masazuka, Takeda assigns Casey and Namiko to guard an old chest called the "Yoroi Bitsu", which contains the suit and weapons of an ancient
Koga ninja. Before Masazuka storms the dojo and murders Takeda, Casey and Namiko manage to take the "Yoroi Bitsu" to
New York City, where they keep it safe at Triborough University's vault with the help of Takeda's friend, Professor Garrison. They are tracked down by Masazuka, who sends Temple's thugs to take down the couple. While Casey and Namiko are on the run, they are framed for the murder of Professor Garrison and arrested. During their interrogation, Casey is ridiculed by Detective Traxler. Disguising himself as Namiko's lawyer, Masazuka slips into the station and cuts the power. He takes down several cops in the dark before incapacitating Namiko. In the midst of the chaos, Casey saves Traxler from being gunned down by Masazuka, who leaves with Namiko. After receiving a tip-off through a member of Temple's thugs, Casey storms Temple Industries, retrieving Masazuka's phone number from the firm's president. He calls Masazuka and sets up a meeting place to exchange the "Yoroi Bitsu" for Namiko's life. Casey then rushes to the university to retrieve the chest and don the ninja suit and the arsenal. At a construction site, Masazuka releases Namiko once the "Yoroi Bitsu" is lowered from a crane, only to discover the chest empty. The two men prepare for a final showdown, but members of The Ring stage an ambush under Temple's orders to kill the trio. Together, Casey, Namiko and Masazuka beat the thugs. Masazuka uses a blowgun to shoot a poison dart at Namiko and taunts Casey with the antidote bottle. However, Masazuka drops the bottle, forcing Casey into a fit of rage. As an
NYPD helicopter flashes its spotlight on the fight, Masazuka uses a
ninjutsu technique to blind Casey with the reflections from his katana and disappears in front of him. Casey uses his instincts to counter-attack and impales Masazuka from behind. Casey is saddened that he is unable to save Namiko. However, upon remembering his sensei's teachings of a ninja's katana possessing the power to both kill and heal, and discovers the antidote inside the handle of his katana. Within seconds, the antidote neutralizes the poison as Namiko awakens. Before they leave, Casey decapitates Masazuka. The next morning, Traxler informs Casey and Namiko that Temple has been arrested and The Ring has been smashed. He gives them their passports and tells them to leave New York City for good. The couple return to Japan to pay homage to their late sensei and continue running their dojo. ==Cast==