三十年代香港，塘西一带歌舞升平，色情、赌博事业发展鼎盛；警察贪污腐败，黑帮当道，奸商横行，百姓苦不堪言，整个社会乌烟瘴气。

时逢拐带案频发之际，自梳妈姐梁芯（杨怡饰）因儿童拐带案报警，刚好案件由杂差邻居金华（张继聪饰） 负责，梁芯深知金华是看钱办事的收规警察，根本无心查案。及后梁芯又见儿童被拐，遇到正义警察沈一然（杨明饰），两人一起找到藏参地点。一然捉拿人贩之际，却被为得暗花的金华偷袭，抢去功劳，二人从此交恶。自此梁芯不齿金华为人，同时对一然的正义感大为欣赏。

富商庄傲山（刘江饰）被人勒索，探长吕国（郑子诚饰）爱理不理，一然自行查探，并未索要任何报酬，令傲山欣赏。及后傲山之子误伤吕国世侄，金华与吕国同流合污，借机敲诈傲山，傲山付款了事，并在吕国面前盛赞一然，但一然却因此被闲置。

梁芯与好友花影月（林夏薇饰）五岁时，被人贩拐卖到塘西欢得妓寨当“琵琶仔”。梁芯不想沦为妓女，屡次偷走不果，直至遇上妈姐梁美兰（程可为饰）好心筹钱替她赎身。相反，影月觉得塘西生活安稳，锦衣玉食，乐于在此享富贵，更成为著名花魁。

Gam Wah appears to be a cop who can easily betray his own dignity and accept bribes. While investigating a human trafficking case, he meets Leung Sam, a woman who has taken a vow of celibacy. Leung Sam and her friend, Fa Ying Yuet, had been kidnapped when they were young, thus, they hate human traffickers. They equally hate corrupt public servants, with the exception of Gam Wah's colleague, Sum Yat Yin, whose upright and honest character catches Leung Sam's eye and she even falls in love with him. Gam Wah and Sum Yat Yin are initially polar opposites, but after Gam Wah's acceptance of a bribe causes the death of a witness, it starts to touch his conscience. However, at the time, the police and the underworld each had their own unbreakable, unwritten laws. Sum Yat Yin is demoted amidst the power struggle of businessman and detective. It puts his relationship with Leung Sam to the test. Seeing all of this, Gam Wah's heart aches, but all he can do is stay silently by Leung Sam's side and secretly hope that he can make up for his past mistakes.