An attempted murder occurred on a rainy night. The victim was being rescued. There was no surveillance or evidence at the scene, and the murderer was at large.The detectives responsible for this case happen to be a father and daughter - Lao He, who is about to retire, and He Ying, the only female detective in the police force. The parent-child relationship between the two has become increasingly tense because of whether He Ying is suitable to continue being a criminal police officer. However, there is a tacit cooperation during the handling of the case.They thought this was Lao He's last case before retiring and could be easily solved, but when they identified all possible suspects, they discovered that Han Dong and Lin Meiyue's family, whom Lao He had interacted with many years ago, were also among them.In order to avoid alerting others, the father and daughter visited all the suspects one by one, and gradually pieced together the unknown secrets of the couple.