Though new to the force, Inspector Fai (Wong Hei) was soon promoted to the investigation bureau of the Customs and Excise Department due to his outstanding performance. He helped break many cases but his subordinate Wa (Bobby Au Yeung) did not seem to work well with him. It took quite a while before the two finally became friends. Inspector Yi (Halina Tam) was the prosecutor for Department. She was beautiful and kind-hearted. She was appointed to work with Fai on a case and they fell for each other. However, Yi was puzzled as she did not want to hurt her boyfriend Man (Harrison Gabriel). Then Fai was sent as an undercover to investigate another case. He was shocked to know the villain behind all the evil deeds was his very own uncle Shan (Chan Wing Chun). How will Fai do?
海關見習督察章浩輝(王喜飾)，原駐守機場關卡，後因表現出色被調往調查局工作。浩輝憑過人的機智，成功偵破一個龐大的私煙集團，但因其處事手法有別於下屬葉天華(歐陽震華飾)，因此誤會頻生。兩人幾經挫折，才冰釋前嫌，建立友情。 海關檢控組見習督察方尚怡(譚小環飾)，被安排與浩輝一同負責調查一宗翻版集團案。兩人因常有接觸而漸生情愫，但尚怡礙於與男友陳健文(海俊傑飾)已有多年感情，不忍離開，使三人的感情停滯不前。 後浩輝獲委任作臥底追查一販毒集團之幕後主腦，經一番努力，揭發主腦是其契舅父余錦山(陳榮峻飾)。