Police officer Ah Mao (played by Chow Yun-fat) discovers a female corpse and a little girl Jia Jia at a gun transaction scene. In order to solve the case smoothly, he found the deceased's sister A Xue (played by Zhong Chuhong). At first, A Xue had an inexplicable fear of A Mao and refused to cooperate with A Mao's work, but later he saw A Mao's careful care of Jia Jia... .