Wendy is an average, popular American teenager. All Wendy wanted was to be Homecoming Queen. Her life is quickly turned upside down after a visit from a young Buddhist monk Shen. Shen informed Wendy that she was not a normal teenager, she was in fact the reincarnation of an all-powerful Yin Warrior, the only person capable of defeating an evil spirit known as Yan-Lo, who attempts to conquer the world every ninety years. Shen begs Wendy to don a powerful amulet that will protect her from evil until he can train her in martial arts.
Wendy is very skeptical of Shen's claims, as well as being appalled by Shen's fashion sense, and pays little attention to him. Wendy goes back to focusing on her campaigning for Homecoming Queen against her rival, Jessica Dawson. Later Wendy goes to the mall to hang out with her friends Tory and Lisa.
Yan-Lo eventually does awaken, and sets out to destroy Wendy before she can attain her full Yin Warrior powers and abilities. The dark spirit possesses a number of people, including Jessica Dawson. While this is happening, Wendy breaks up with her boyfriend, Austin after realizing how rude he is, and starts to bond with Shen. With Shen's help, Wendy's teachers are temporarily possessed by the souls of the Five Animals of Chinese martial arts to help teach Wendy. Mr. Medina becomes the Tiger, Coach Gibbs becomes the Snake, Mr. Tobias becomes the Crane, Mr. Garibay becomes the Leopard, and Shen himself becomes the Dragon. The martial arts training unleashes Yin-Warrior within Wendy for a final confrontation with Yan-Lo during Homecoming.
Wendy frees Jessica from Yan-Lo, who thanks her for lending her the Homecoming crown and the Queen status, before leaving apparently unaware of being possessed. Yan-Lo then returns, choosing to this time appear in person, and the battle continues. Shen attempts to sacrifice himself, but Wendy saves him by changing his destiny. Wendy and Shen then defeat Yan-Lo together, and Yan-Lo is destroyed forever. The monks tell Shen this is his last life, and leave. Wendy then invites Shen to have a cappuccinos and chocolate to celebrate their victory.