In Paris, France, a hired assassin, disguised as a mother pushing a baby carriage, and an accomplice kill a Canadian diplomat in front of his home. The killer escapes, but her associate is gunned down. At a theater in Los Angeles, California, Scott James, a retired martial-arts champion, and his fellow fighter-friend, A. J., go backstage to meet dancers after the performance. Nancy Bell agrees to go to dinner with Scott, and expresses concern when she sees the newspaper story about the Canadian diplomat’s murder. Later, Scott escorts Nancy home, and they are ambushed by ninjas. Scott overwhelms several attackers, but Nancy is knifed in the stomach. Meanwhile, at an overseas ninja training camp, Seikura, its terrorist leader, outlines the harsh rules of the organization to the new recruits. In Los Angeles, Scott recounts the attack to A. J., who tells him newspapers report that Nancy’s brother was responsible for the Canadian diplomat’s murder. Later, Scott visits his friend, McCarn, who hears his story and insists that ninjas were outlawed 300 years ago, and no longer exist. Nevertheless, Scott asks McCarn to inform him if he sees or hears anything strange. On his way back to town, Scott stops to help a stranded female driver named Justine. After pushing Justine’s vehicle back onto the road, he realizes that she has accidentally taken his car keys. When Scott finds her, Justine returns his keys and insists on taking him back to his car. Later at the docks, A. J. tries to question a friend of Nancy’s brother named Johann, but he runs away. McCarn’s associates strangle the fleeing man, and McCarn warns A. J. not to contact the police. As Scott and Justine drive, they are ambushed by a sports car and a limousine. They escape and Justine reveals that her father, a European publisher, was killed by terrorists, and she has inherited his fortune. When terrorists threatened to kill her unless she changed editorial policies, she moved to America. Later, Scott arrives at Justine’s home to take her to dinner. He learns that she hired McCarn’s men because she was told that Scott would not be willing to destroy his estranged Asian brother Seikura. Justine hopes that her charms will convince Scott to help her, but he is insulted and leaves. Walking to his car, Scott refuses to believe Seikura is responsible for the recent violence. Meeting at a bar, A. J. informs Scott that Nancy was an operative for a terrorist group and couriered money for their causes when she toured overseas with her dance company. A. J. is convinced he can do a better job controlling terrorists than the police, but Scott warns him it is too dangerous. In private, Scott makes arrangements with a man named Mr. Beatty to take an assignment as a mercenary soldier. He recalls the time that Isawa, his adoptive Asian father, banished Seikura after he tried to claim a sword that Scott had won in competition. When Seikura refused to ask forgiveness, Isawa warned Scott that Seikura dishonored the family and to never again speak his name. Justine interrupts Scott’s thoughts at a restaurant, and again tries to persuade him to help her. A. J. interrupts their conversation, and is attracted to Justine. Scott excuses himself and leaves. As the new ninjas complete Seikura’s training, they are warned they will be killed if they break the ninja code. Scott arrives at a mercenary compound in the desert, where the supervisor, Doggo, and his assistant, Aura, interview him. When Scott expresses a desire to be trained by Seikura, Doggo tells him he has no knowledge of the ninja leader. Meanwhile, Aura refuses an assignment in Egypt, steals Scott’s file, and defects from Doggo’s compound. She waits for Scott at his hotel apartment, and explains why she needs his help. Soon, Justine arrives and informs Scott that A. J. is missing, but she is not telling the truth, and Scott refuses to help her. In the building lobby, Justine wants A. J. to call off his search for Seikura, but he ignores her and hails a taxicab to the airport. A terrorist kills Justine with a poison dart. After Justine’s death, Scott changes his mind and sets out to find Seikura, while Aura agrees to help. As A. J. observes Seikura’s camp from afar, he is captured. Soon, Scott approaches Seikura’s compound, and orders Aura to stay behind. He sneaks into the camp, and fights several men before Seikura puts him to the test on an obstacle course, where he fends off more attackers. Soon, Scott and a ninja engage in a sword fight. From a tower above, A. J. throws a burning torch into the courtyard. As Scott pushes the ninja into the fire, Seikura’s men slit A. J.’s throat, and throw his body at Scott’s feet. Seikura and his men then descend into the arena to fight Scott. Terrorist recruits kill a ninja fighter, and the other ninjas chase them, leaving Scott and Seikura to fight each other. Meanwhile, Aura, with help from terrorist recruits, sets fire to the compound. As day breaks, Scott kills Seikura, and the fight is over.