In the late 1970s, a young police officer Wang Xin mistakes old railway policeman Ma Kui as a fugitive on a steam train from Ningyang to Harbin. However, their conflict evolves into a mentor-apprentice friendship. They work together on the front line of railway security, tackling theft, kidnappings, drug trafficking, and fraud. As they prioritize passenger safety, they witness the transformation of China's railway system from steam to electric and high-speed trains. Wang Xin and Ma Kui uphold the spirit of the police and experience China's rapid changes.