The play is adapted from Shuang Xuetao's novel of the same name, telling the story of an old story revealed by a murder of a taxi driver. Zhuang Shu (played by Dong Zijian), a rebellious teenager, becomes a criminal policeman and is responsible for investigating an old case from seven years ago. The suspect gradually points to the neighboring father and daughter who left him with good memories in his childhood. As the investigation deepens, a cigarette butt sheds light on the case, and the criminal policeman sadly discovers that he may have been a participant in the tragedy that year.