School resumes after summer vacation. Some of the Form 4D students are punished by the principal for ill-discipline. Form 4A despises them as a class of poor records. Form 4D is going to strike them back an eye for an eye. Being the class-mistress of Form 4D, CHING is held responsible for their demerit. Owing to the silence of the Form 4D students, there is no clue for investigation.

BONG comes back to Hong Kong to continue his studies. He lives in DOCTOR NGAI, his guardian's house. BONG feels hard to adapt since NGAI is a very strict man. He enters Form 4D under the arrangement of NGAI. BONG is mistaken as the spy sent by CHING, so he is isolated by his fellow classmates. The guys trap BONG by a silly trick. CHING is anxious to learn the truth.