A sixth-grade student named Aya Tachibana is prone to worrying about her loved ones, academics, and other issues. However, everything changes when she becomes a member of the "Tantei Team KZ," a group of four unique boys she meets at a cram school. Kazuomi Wakatake is the charismatic and flashy leader, Takakazu Kuroki is the enigmatic relationship expert, Kazunori Uesugi is the reserved math genius, and Kazuhiko Kozuka is a compassionate master of social affairs and science. Aya discovers that her particular talent is being the "language expert" among the group. Together, they solve modern-day cases, often clashing but always utilizing their individual abilities.