The father of a Taiwanese teenager named Puppy (played by Aaron Kwok) informed the police, causing the Taiwanese gang boss to be temporarily imprisoned and awaiting prosecution. For safety reasons, Puppy came to Hong Kong and changed his name to attend St. Yuqiang Middle School. Negotiation expert Ajian (played by Zhang Jianting) was sent to St. Yuqiang Middle School as an undercover teacher to find Puppy because he often made mistakes in negotiations. Ajian came to St. Yuqiang Middle School and found that the students here were all naughty and problem teenagers, among which the student leader A Shi was even more troublesome. Ajian met the female teacher Mengxiang (played by Zhang Min) at school and soon developed a good impression of her. At this time, Ajian's girlfriend, policewoman Aqing (played by Qiu Shuzhen) also came here as an undercover. Ajian, who was already unable to cope with the naughty students, was also facing a love triangle, and the school was full of hilarious scenes. The Taiwanese gang boss was finally released due to insufficient evidence. After killing Puppy's father, he came to Hong Kong to kill Puppy. Facing the Taiwanese gang, can Ajian finally save Puppy successfully?