A clan of ninjas finds an abandoned treasure chest that had been washed onto shore, inside of which was a white infant boy. An ancient legend spoke of a foreigner who would come among the ninja and become a master like no other. The white orphan boy, Haru (Chris Farley), is raised among the ninja, with the expectation that he may be the one of whom the legend speaks. As Haru grows into adulthood, doubts are quickly cast over him for being the great white ninja. Although he does possess some ninja traits, Haru is clumsy and does not really fit in, and fails to graduate a ninja with the rest of his class. Left alone to protect the temple while the clan are on a mission, Haru disguises himself as a ninja when a blonde American woman who comes to seek the services of one. The woman, Sally Jones (Nicollette Sheridan), is suspicious of her boyfriend, Martin Tanley (Nathaniel Parker), and sends Haru to a Tokyo harbor to investigate.Haru finds out that Tanley and his staff, Nobu (Keith Cooke Hirabayashi) are involved in a counterfeiting business and also witnesses a murder. The clan are disappointed with Haru's actions when Tokyo police presume that Haru is responsible for the murder. However, Haru admits that Sally was in trouble, despite her name is a pseudonym. Haru departs from Tokyo to Beverly Hills to search for Sally. Gobei (Robin Shou), Haru's adoptive brother and the best ninja in his class at the beginning of the film, is sent by the clan to watch over and protect Haru.Haru has trouble adjusting to Western culture, but checks in at a Beverly Hills five-star hotel, where he befriends an employee, Joey Washington (Chris Rock), and teaches him some ninja lessons. Haru sets out on his search for Sally, convinced that she is in trouble. Haru eventually finds Sally, but she distances herself from him. Haru tracks Tanley and Nobu to a night club in Little Tokyo, where they are trying to get back a set of counterfeiting plates from their rival gang. Unfortunately, Haru finds himself as the suspect of a second murder. He return to the hotel the next day and meditates to communicate with his Sensei (Soon-Tek Oh) for guidance. Haru resumes his quest, and tracks down Tanley's mansion. Upon entering Tanley's mansion, Haru speaks with Sally, whose real name is Allison Page. He eventually begins to trust her again, and Allison tells Haru that she accused Tanley for killing her sister.That night, Haru and Allison escape a gun-fight at a Japanese restaurant, where Tanley and his henchmen sees Allison there. Haru and Allison have their retreat at the hotel for the night. The next day, Haru disguises himself as ink specialist Chet Walters (William Sasso) and Tanley takes him to his warehouse, where Tanley soon finds out that Haru is "the fat ninja that everyone is talking about". While Tanley is in the process of getting the other half of the plates that night, Allison rescues Haru from the back of Tanley's van. However, Tanley kidnaps Allison during the process, and Haru must find his way back to Tanley's warehouse to rescue Allison, but since he was blindfolded during his first trip, Haru must recreate his ride by memory and enlists his help of Joey and without knowing that Gobei is also hiding in the trunk. After Joey accidentally drives the convertible through a horse race and a car wash, he and Haru start over. Gobei gets out of the trunk after Haru is blindfolded, knocks Joey out, and drives the convertible to Tanley's warehouse. Haru uses the momentum of a large palm tree to jump into Tanley's warehouse, while Gobei also makes it in by using stealthier methods.Haru and Gobei fight Tanley's henchmen until Haru is reminded that he should be rescuing Allison. Using a forklift, Haru smashes two holes in the wall of the room where Tanley takes Allison hostage, almost setting off the bomb. Haru attempts to defuse the bomb, but accidentally resets it for five minutes. Haru leaves Allison for four minutes to help Gobei, who is surrounded by Tanley's henchmen. Haru jumps off the railing and eventually lands on an ax-wielding henchman who attempts to kill Gobei and suddenly becomes an adept ninja when Gobei gets hurt by Nobu and his henchmen. Haru and Gobei defeat one henchman with their little help from Joey, who jumps into Tanley's warehouse and eventually lands on one of them. Haru and Gobei has two minutes to defeat Tanley, who has a gun. Haru cuts the rope of a winch to aim for Tanley, but the hook accidentally knocks out Gobei instead.Blocking Tanley's bullets by swinging his two swords, Haru eventually incapacitates Tanley. He return to the upper level to rescue Allison. Using a huge harpoon gun mounted on a cart, Haru shoots a harpoon through the room and inadvertently lands in the back of a truck where Tanley attempt to escape from his warehouse. After capturing the bomb, the cart lands in Tanley's truck and explodes seconds later. Haru successfully rescues Allison, and Tanley and his surviving henchmen are arrested.In the film's conclusion, Haru talks to his Sensei about returning to Beverly Hills, where they do not have ninjas there. Haru and Allison later ride on the bus, which accidentally drags a rope tied into Gobei's wheelchair. Haru shouts an apology to Gobei, who is thrown into the ocean.