A woman is murdered in the street. Before she dies, she writes down the three characters "Chen Xuelin." It seems the killer is right before the police, but they discover that the message left by the victim appears to point to a university professor who died many years ago.
An investigation reveals that Chen Xuelin was a respected person in life. Somehow, however, she was murdered by one of her own students. As the investigation deepens, Li Zhong, captain of the criminal investigation team, realizes that her death was not a heroic act meant to prove the victim's innocence. She did it to expose the victim's crimes, because she could not let them go.
