en Cuevana 3. High school student Yoshiro Kobayashi (Mahiro Takasugi) is the great-grandchild of the first president of the Boy Detectives Club. He enjoys time with his friends Watari (Gaku Sano) and Saya (Mayu Hotta). One day, the Fiend with Twenty Faces appears in front of Yoshiro. Mysterious cases then takes place in sequence.