Heartless and smart Mo Ching was a crippled since he was a baby. Luckily, Chu Kot Ching Ngo, the Head of Sheriff Bureau saved him and thought him exceptional skills of using concealed weapons. Emperor Sung was grateful to Chu Kot as he had helped the Emperor to repossesses an important relic that was lost. To reward Chu Kot, the Emperor decided to reopen the Sheriff Bureau. Chu Kot recruited four constables to work with him in the bureau. They are Mo Ching, Zhui Ming (a cunning conman), Tit Sau (an honest and kind man) and Lang Huet (an aloof yet agile but cold-blooded man). They are collectively called "The Four".
Under the leadership and guidance of Chu Kot, the Sheriff Bureau has solved many difficult cases. After experiencing the trials and tribulations with the other 3 constables, Mo Ching has learnt to be more humble and less arrogant. he soon develop feelings for Sung Zhi Yan, a physician. However, Zhi Yan manipulate Mo Ching's affections and seize this opportunity to break up the team. Zhi Yan intentionally create a rift between Mo Ching and Tit Sau.

Chu Kot himself is also stuck in a precarious position, trying to expose the rebellion of Wong Chiu Cheong and Choi Ging, risking his life and driving himself away from The Four.