A group of criminals call themselves the "Northern Detachment". They commit several major crimes on the Beijing-Guangzhou Railway. The Public Security Bureau sends Ma Xiaolong after them.

After school, Xinhua Primary School was quiet until Principal Lin Zheng heard arguing between fifth-graders Hua Xiaochuan and Fang Mingzhu. Fang was supervising Hua, who was late, as he did chores. Hua’s friend Zhang Chen wanted to help, but Fang refused, causing an argument. Principal Lin believed labour as punishment was ineffective and should be replaced with work-study programs, as instructed by the municipal party committee. He assigned Hong Dawei to lead the program, but Teacher Jiang opposed it, emphasising classroom education. Despite initial resistance, students participated in tire-moving labour, training teachers, parents, and students. Three students took sick leave, fueling Teacher Jiang’s objections. Principal Lin and the academic director found some parents were overly indulgent. Secretary Liu commended their efforts and encouraged them to continue.

In Japanese-occupied Harbin, young officer Feng Jiangchu investigates a mysterious "Ghost House" after a thief is found dead inside. Undeterred by warnings, he delves deeper into the case, uncovering a complex web of intrigue involving the Japanese forces and resistance fighters.