Star Chow is a highly skilled and dedicated police officer who has a reputation for being always ready to take on dangerous missions. However, his unconventional approach to police work often lands him in trouble with his superiors. When Star is implicated in a minor scandal at the SDU, he is demoted and given one last chance to redeem himself.
Star's new assignment takes him to Edinburgh High School, a prestigious institution in Hong Kong. His mission is to recover the senior officer's stolen revolver, which was allegedly taken by a student. Star plunges into his undercover role with enthusiasm, but he soon realizes that he is in over his head. The school is a hotbed of student politics, with rival gangs vying for power and influence. Moreover, Star is partnered with Tat, a bumbling detective who seems to be more interested in eating than in solving crimes.
Despite these challenges, Star soon discovers that he has a talent for teaching. He uses his exceptional martial arts skills to win over the students, who are initially resistant to his authority. He also becomes involved in a romantic relationship with Ms Ho, the school's guidance counselor. However, Star's cover is jeopardized when he accidentally exposes his true identity. The gang involved in arms dealing, finding him as an obstacle, tries to kill Star and disrupts the delicate balance between the two rival student gangs.
As the climax of the movie approaches, Star realizes that he has not only fallen in love but has also discovered that Tat has been working undercover to catch Ms Ho's killer, Tsui. Finally, in a thrilling finale, Star works with Tat and the students to bring the gang to justice and recover the stolen revolver. The movie ends with Star being reinstated to the SDU, and his future with Ms Ho uncertain due to his reckless nature.