Four police officers are blood brothers. One day, the fourth brother is killed mysteriously. The others are very upset. Another police officer (Kai) is responsible for this murder case, and he finds out that the second brother was the murderer. But, why does Kai resign after this case is closed?四名警察是結拜十多年的兄弟。破獲毒品案後，他們把部份贓款均分。老四突然被殺，同僚都深感惋惜。在凶殺案現場，重案組警員冼佳發現一些蛛絲馬跡，與下屬白玲深入調查。冼佳以白玲為餌，設局引凶手上釣。凶手終於落網，竟然是老二！他不滿老四為了升職而出賣兄弟，於是動了殺機。冼佳破了殺警案後，忽然辭職......
