Four junior high school students gathered by a mysterious invitation. After successfully overcoming the ordeal of an old man named Jean-Paul, they are recognized as the "Boy Detectives". Knife user Sosuke Hashiba, fighting girl Kyoko Nanatsugi, famous hacker Kentaro Kanzaki, and dual personality girl Mika Yumeno. Rumors of the monster Skull King and the monster θ (Theta) are disturbing the big city of Shinjuku... In order to confront their suspicious and evil intentions, they decided to work as the "Boys Detective Group".