High school student Saya Toma lost her parents and younger brother in an airplane accident and one day she was told that her family has a high possibility that they were killed by people who have spec.
6 years later, Saya decides to become a detective. She returns to Japan after receiving training by the FBI in the United States and she is assigned to work unsolved cases in the Public Security Bureau.
Meanwhile, because of Satoshi Chii';s scheme, Juichi Ninomae considers Saya Toma his parents'; enemy and tries to push her to the edge. Satoshi Chii';s scheme has also caused Saya Toma and Juichi Ninomae to forget that they are brother and sister. The siblings are headed to a life-staking fight.
A girl named Maho Ueno becomes involved in their fight. To protect Maho Ueno, Saya Toma uses "spec".