Natsuki Amakusa is a gifted young detective serving with the Tokyo Metropolitan Police Department. One day, he encounters Yuuya Shiki, a high school student who possesses a mysterious ability to see "marks" on murderers. Following Yuuya's assistance in solving a complex murder case, Natsuki decides to recruit him. The two form a partnership to investigate various criminal cases, all while working to uncover the mystery behind Yuuya's hidden power.