This story focuses on two "over zealous" policemen. The movie begins with an academic exhibition, due to Yuen Biao "neurotic" behaviour, both Yuen and his supervisor, Captain Mean, are heavily penalized. Lowell Lo is in the midst of a car chase that gets himself involved in a heated argument with police. As though the protagonists are destined to be partners, both of them are transferred to the C.I.D. Captain Mean assigns them a difficult case - "The case of the missing informer". The last person known to have contacted this informer is his girlfriend Lok Siu Fan whom is known as Rosa. During the investigation Yuen Biao falls in love with Lo's sister Wai Ying Hung and Lo becomes attracted to Lo Siu Fan. Eventually, they unravel the mystery behind the case. (Joy Sales)