In 1978, on a train from Dalian to Sankeshu, young police officer Wang Xin was injured in an arrest operation on his first duty, but he met Ma Kui, an old criminal police officer of the railway public security, and the two became master and apprentice, fighting side by side on the front line of the railway public security. On this railway line, they have experienced the era of steam locomotives, electric locomotives, and high-speed rail in the past 40 years, and witnessed the great achievements of the motherland and the tremendous changes in people's lives. The front-line railway police officers represented by Wang Xin and Ma Kui fight pickpocketing, fight abduction, fight drug trafficking, patrol the line, guard, fight theft, robbery, and fraud, and eliminate gangs and evil. For decades, they have solved major cases, solved minor cases, brought warmth to passengers, and lived in harmony. In order to protect the lives and property of the people, the railway police officers even sacrificed their precious lives. The passengers coming and going on the train carry different marks from different periods, showing the warmth and coldness of human feelings and the various aspects of life. The new and old generations of police officers have also been sublimated in their life experiences, loyal police spirits, and passed on the torch.