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Saya Toma (Erika Toda), a high school student, lost her parents and younger brother in an airplane accident. Detective Akio Kondo (Yu Tokui) arrived and informed her that "your family has a high possibility that they were killed by people who have spec." That was her first encounter with the term "spec." Saya Toma, who has never forgotten what the Detective said, decides to become a detective 6 years later. After receiving FBI training in the United States, she returns to Japan. Saya Toma is assigned to the Public Security Bureau to work on unsolved cases. Meanwhile, as a result of Satoshi Chii's (Yuu Shirota) plot, Juichi Ninomae (Ryunosuke Kamiki) regards Saya Toma as his parents' enemy and attempts to push her over the edge. Satoshi Chii's plan has also made Saya Toma and Juichi Ninomae forget they are brothers and sisters. The siblings are about to engage in a life-or-death battle. Maho Ueno (Umika Kawashima), a girl, becomes involved in their fight. Saya Toma employs "spec" to protect Maho Ueno.