CID officer Lai Yat-tsau (Bosco Wong) parents died early, leaving him to take care of his three younger sisters. First younger sister Lai Suk-chu (Kayi Cheung) is a prestigious kindergarten school superintendent who is kind but gullible. Middle younger sister Jil Lai Suk-si (Tracy Chu) is a luxury brand salesperson. She is immature and money hungry. She originally dated Yat-tsau's partner Fai Chung-lim (Raymond Wong) because he is a rich restaurant heir, but after years of dating she really fell-in-love with him and wants him to quit the police force because of the dangers that comes with the job, also for him to return to being a rich heir. Youngest sister Fanny Lai Suk-fan (Angel Chiang) is rude and lazy, who refuses to find a job. She is also the only one in the family that is married. Her husband Ma Chi-chung (Oscar Leung) works at the Agriculture, Fisheries and Conservation Department, but his attitude is very similar to his wife and often mooches off of his in-laws. Lai Yat-tsau is a reckless cop who does major damages to the streets of Hong Kong when he is chasing crooks. His recklessness drags his partner Chung-lim down with him. Together the pair are nicknamed "Faw Sui" Sir (which means "Kerosene" in Chinese) and "Fai Chia" Sir (which means "Firewood" in Chinese) because the two are tend to start a fire. When Yat-tsau's former informant Lui Kam-bo (Jerry Ku) seeks his protection from his recently released older twin brother Lui Kam-dong (Jerry Ku), that Kam-bo had helped Yat-tsau put in prison. Yat-tsau trails Kam-dong's every move to make sure he doesn't kill Kam-bo. During a drug bust between Kam-dong and his former gang, Yat-tsau gets attacked by the gangs guard dog named Bah-da (Hong Kong saying of the English word "Brother"). While recovering from a dog bite in the hospital his meets Ma Chi-ho (Linda Chung), who is more concern for Bah-da then Yat-tsau's injuries. Chi-ho's political correctness and bluntness ends up offending Yat-tsau which leads to the two becoming enemies. Ma Chi-ho is a veterinarian for the Agriculture, Fisheries and Conservation Department. Her love for animals overshadows her consideration for others and her blunt know it all attitude offends people she speaks to. Due to her love for dogs she became estrange with her mother Madam Chung, who is also Yat-tsau's new supervisor, when her mother had her police dog euthanized. Her younger brother who also happens to coincidentally be Yat-tsau's brother-in-law Chi-chung works alongside her, but he too can't stand her because she made him feel stupid when they where growing up. To prevent Bah-da from being euthanized, Chi-ho must find a reason proving he is not a dangerous dog. When Bah-da sniff out an Agriculture, Fisheries and Conservation Department employee with drugs on him, Chi-ho realizes that Bah-da knows how to detect illegal substances and recommends that Bah-da be train as a police dog. Madam Chung also forces Yat-tsau's to transfer to the Police Dog Unit so that he can learn some disciplinary.