After ten years behind the bars in Taiwan, Kong Sai-Hao finally returns to Hong Kong. Besides hoping to find his daughter Yau-Yau to mend their relationship, he also plans for revenge. On one hand, he pretends to surrender to triad boss To Yik-Tin, the man who caused him to be jailed. On the other hand, he tries to gain trust from police officers Chung Lap-Man and Lee Pak-Kiu. Pak-Kiu refuses to have a criminal as his friend, but Lap-Man becomes a undercover cop in Sai-Hao's gang. Along with Sai-Hao, they overrule Yik-Tin and take over the mafia, and the two develop a misconceived mentor-student relationship. Unfortunately, Lap-Man gets fired from the police force before he can finish his mission in the mafia. He becomes Sai-Hao's people and turns his back against the police force.

本剧是学警系列的第三部曲，学警经训练及在机动部队工作後，将参与警队的实际工作。让观众一起经历警员们的成长过程，由受训到成为一名维持社会治安的警员，当中经历多少辛酸、挣扎及矛盾，为观众一一道来。

社團中人江世孝從台灣服刑回港，四處打聽愛女江悠悠下落之餘，不忘部署復仇。世孝向當年害他入獄的龍頭大哥杜亦天假意投誠，又誘導警員鍾立文及李柏翹成為自己人。柏翹堅拒與賊為友，但立文卻深信可將世孝轉為警方線人，二人逐步建立兵賊錯位的師徒關係。亦天對世孝常存戒心，安插親信梁笑棠挾制其勢力，世孝伺機利用亦天之妻程若芯在社團的影響力登上龍頭，販毒生意卻連遭滑鐵盧，始發現最信賴的身邊人比他更懂背叛、欺騙、出賣。

Sau 10 năm ngồi tù, đại ca giang hồ khét tiếng một thời Giang Thế Hiếu trở về mang theo âm mưu trả thù những kẻ năm xưa đã hãm hại y. Kế hoạch của Hiếu còn kéo theo lực lượng cảnh sát cùng trùm xã hội đen Đỗ Diệc Thiên rơi vào cuộc chơi tay ba gay cấn. Cuộc chiến phi nghĩa này sẽ kết thúc ra sao? Mời các bạn theo dõi bộ phim.