On the day he joins the Police Discipline Unit, Liu Chen-hui meets his old classmate Cheng Chin. In a chat they talk about their childhood. From the conversation, Liu observes that the police force in the unit is slothful and decides to boost their discipline.

Liu spots one of his subordinates introduced by his superior to be his ex-brother-in-law Chou Chuan -- divorced by his wife Mei-chen due to addiction to gambling. He subconsciously antagonizes him and often finds excuses to baffle him.

Cheng Chin nabs an addict Cheng on charges of hiding heroine. In retaliation, Cheng, who has been Chou Chuan's informer, deliberately offers information of a gang robbery on a jewellery shop before informing the thugs to delay their holdup.

Acting on the tip-off, Cheng Chin and the others lay an ambush for the thugs without finding any trace, and are reprimanded by their superior for wasting manpower.… ...