Trainee constable Su Xiaoqiao switches identities with Gu Qingdai, the widow of a bandit leader, to investigate her mother’s murder. Posing as Gu Qingdai, Su Xiaoqiao takes control of the bandit stronghold and is forced to marry Chu Yan, her undercover superior from the Suzheng Office, as part of her mission to uncover a conspiracy.

The film takes the "slow train" driving deep in the mountains and the conductor's boring work position as the carrier, through the main character Cheng Lu, Zhao Dapeng and to Pingping two young college students and young conductors