This drama is adapted from the manga of the same name, and tells the story of the discovery of the skeletal bodies of 13 children, commonly known as the "Gray River Residence Incident". The mysterious sign left at the scene reappears after 7 years. The incredible life together, the suspect called "father", the 6 survivors of the incident, and the truth that is somewhat hidden. The endless mysteries lead people to an unpredictable ending...