Enduring the hardship of his father’s drug addiction and his mother’s death, hot-headed cop LAI YAT-TSAU (Bosco Wong) single-handedly raises his three younger sisters. Due to his domineering personality and short temper, he is transferred by his boss to the K-9 Unit to undergo a grueling training session together with a police dog, yet in the process, a misunderstanding causes him to have a bitter feud with MA CHI-HO (Linda Chung), a veterinarian for the Agriculture, Fisheries and Conservation Department (AFCD) and the police. Surprisingly, CHI-HO takes the initiative to help YAT-TSAU and his canine partner overcome obstacles in the hope of seeking YAT-TSAU’s support in bridging the rift that’s grown between her and her younger brother MA CHI-CHUNG (Oscar Leung).
Meanwhile, with the human-canine bonding, not only does the chemistry between YAT-TSAU and CHI-HO sparkle, but YAT-TSAU also feels more confident of hunting down the notorious drug dealer LUI KAM-TONG (Jerry Ku). Unfortunately, YAT-TSAU’s partner FAI CHUNG-LIM (Raymond Wong) breaks a rule by concealing his illness, resulting in their brotherhood breakdown. On top of that, CHUNG-LIM’s action even gets his girlfriend LAI SHUK-CHI (Tracy Chu), who is also YAT-TSAU’s second younger sister, involved with her life at stake. Fueled by an unquenchable thirst for vengeance, KAM-TONG manipulates his twin brother LUI KAM-PO (Jerry Ku), a police informant, to plot a setup against them. How are YAT-TSAU, CHI-HO and the K-9 cop going to solve the case together and save lives?