Yes, Sir. Sorry, Sir!(2011)

series - first aired/released 2011-05-05 - audience 8.0

How hard can it be to go back to your old job? Law Yiu Wah (Moses Chan) was a teacher at a dangerous high school before he was forced to resign over a peeping Tom controversy. Wah becomes a police officer but then is asked to go back to his old high school to investigate a triad drug network at the school.