A murder case involving a child victim occurs near the Han River. Jin-Soo, a detective whose life has been in shambles since his own daughter was kidnapped and killed, is assigned to this case. Obsessed with child-related cases since his own tragedy, Jin-Soo becomes deeply engrossed in the investigation. One day, Jin-Soo is approached by his high school classmate, a famous actress, who asks him to find her missing sister. As he investigates, he discovers disturbing connections between her and the child found by the Han River. Unsettling truths gradually begin to unravel.