Tobita Tasuku's father, Jinpei left a letter and disappeared on the day of Tasuku's high school graduation. Due to his father's disappearance, Tasuku is now left with his father's huge debt while he is still unemployed. Tasuku decides to visit the Joker Detective Agency to find his father but the cost of investigation is too high. Tasuku later finds out that the tuition fees for attending the detective school is much cheaper than the cost of investigation. Seeing that he can get a job in a detective agency and find his father, Tasuku decides to enroll into the Joker Detective School and be a full-fledged detective.