Cheng Shengyuan discovers the strange habit of his live-in roommate, Xu Man, who frequently changes the bedding. His older cousin discovers that the bedding is contaminated with dangerous, prohibited experimental substances, but an accident occurs during the investigation. Following the clues, Cheng Shengyuan learns that both his father's old case and his younger brother's unusual physical condition are connected to the substances. Xu Man is actually a member of an international illegal research syndicate conducting secret experiments there. Cheng Shengyuan cooperates with the police to rescue his younger brother, stages a confrontation to record a confession, and prevents an explosion. The criminals are arrested, and the criminal network is dismantled. A year later, the brothers move into a new home and leave the darkness behind.