The film is based on the real-life experiences of Zhang Huiling, a police officer from the Shuangyushu Police Station of the Haidian Branch in Beijing.

Veteran plainclothes officer “Old Zhang” (played by Zhang Lixian) shares drinks and songs with his colleagues, expressing the bittersweet realities of life in Beijing. Beneath this seemingly relaxed exterior, however, he and his team are constantly on duty—blending into the bustling crowds, waiting for the right moment to apprehend criminals. From thieves who use electronic devices to unlock cars, to scammers who exploit disabled individuals for staged accidents, to organized burglary rings and fraudulent fortune tellers—none can escape Old Zhang’s sharp eye. His work even becomes the subject of a television documentary in Beijing.

Yet as more and more criminals are brought to justice, Old Zhang finds himself increasingly conflicted. He is, after all, an ordinary man with aging parents and a family to support. Years of relentless work have taken a toll on his health—he suffers from asthma and high blood pressure—but he continues to push through his physical limitations in pursuit of justice.

At the same time, a mysterious figure persistently follows him, and a series of strange and unpredictable incidents begin to unfold, catching Old Zhang and his team off guard. As reality and uncertainty intertwine, the film presents a raw and human portrait of a policeman navigating duty, vulnerability, and the complexities of urban life.