A friendship falls apart after the disappearance of a girl.

On 1949 October 1, the day of the founding ceremony of the People's Republic of China, Xiao Dali enters the city and is reorganized as the director of the public security police station. He finds that primary school teacher Feng Jingbo is full of doubts. With the high vigilance of a soldier and the sense of responsibility of a public security official, Dali insists on partnering with Feng and becomes his neighbor. He then spends his whole life carrying out a nearly four-decade pursuit without regrets.

Our story begins on the last day of school during final exams in Beijing, China. Mouth, a shy insecure 15-year-old, and his best friend Monkey, an undersized energetic loudmouth, get ready ...