Aya Tachibana is a sixth-grader who frets and obsesses over friends, family, grades, and more. One day, she joins the "Tantei Team KZ" with four very idiosyncratic boys she met at cram school. There is the glib and attention-grabbing leader Kazuomi Wakatake, the mysterious "expert of personal relationships" Takakazu Kuroki, the smart and stoic math genius Kazunori Uesugi, and the sweet-hearted Kazuhiko Kozuka, who is good at social matters and science. Aya finds her place among them as the "language expert." "Tantei Team KZ" gets involved in modern-day cases, and even if they bicker from time to time, they collaborate by pooling each of their talents and skills to solve these cases.