A 20-year-old unsolved murder mystery of a young girl happened again 20 years later, which aroused the memories of the people in the seemingly peaceful town. The once young Shanfeng (played by Song Yang) grew up to be a policeman and returned to the town. The painful memory that could not be erased made Shanfeng chase the murderer again. In his search for the truth, he found that not only himself, but all the people involved in the case had undergone earth-shaking changes because of this mystery 20 years ago. The night in the riverside town was like water, and on the foggy road of chasing the murderer, there were repeated tortures of human nature, and unexpected crises and answers.