After losing both parents at a young age, Lai Yat Tsau becomes a parent figure for his three younger sisters. His mother’s death and his father’s fall to drug addiction turned Yat Tsau into a very quick-tempered and chauvinistic man. Originally assigned to the Kwun Tong Police Station, Yat Tsau’s superior transfers him to the K-9 unit to work with police dogs, hoping that the strict training would better shape his character. Yat Tsau is appointed to work with a K-9 called Brother, but Brother does not take a liking to him. During this process, Yat Tsau steps on the wrong end of veterinarian Ma Chi Ho, and the two strong personalities clash. But Chi Ho, who needs Yat Tsau’s help in mending her estranged relationship with younger brother Ma Chi Chung, volunteers to aide Yat Tsau in improving his relationship with Brother. Through Brother, Yat Tsau and Chi Ho develop an interesting partnership and chemistry. With Chi Ho’s help, Yat Tsau and Brother bond. Brother also helps Yat Tsau track down the drug dealer Lui Kam Dong. Just as he is closer to solving the case, Yat Tsau’s partner and close friend Fai Chung Lim breaks an unwritten rule in order to keep a secret, putting a dent on their brotherhood. This also gets Chung Lim’s girlfriend and Yat Tsau’s younger sister, Jil, into a near-fatal disaster. Kam Dong returns for revenge and uses his younger twin brother Kam Bo, who has been working as an informant for the cops, to concoct a trap. Yat Tsau, Chi Ho, and Brother team up to save their friends.