Set on year after the fight between detectives Saya Toma (Erika Toda), Takeru Sebumi (Ryo Kase) and Satoshi Chii (Yuu Shirota). More confrontations ensues between the detectives at the Unidentified Crimes Unit of the Tokyo Metropolitan Police Department. Takeru Sebumi (Ryo Kase) returns after taking a break due to his eye problems. Kenzo Ichiyanagi (Denden) is appointed section chief, while Kotaro Nonomura (Raita Ryu) is demoted. New member Shu Yoshikawa (Kazuki Kitamura) joins the team.

Saya Toma (Erika Toda) is a female detective with an IQ of 201. Takeru Sebumi (Ryo Kase) is a career detective with a distinguished background. They work on cases by postulating the "SPEC" of the unknown criminals and then deduce the criminal's unknown "SPEC" to make arrests. A mystery occurs when bodies are found on a cruiser in the ocean. Saya Toma and Ryo Kase of the Tokyo Metropolitan Police Department are brought in to solve the case.

A prequel to the series. High school student Saya Toma lost her parents and younger brother in an airplane accident. Detective Akio Kondo came and told her "your family has a high possibility that they were killed by people who have spec." That was the first time she heard of "spec". 6 years later, Saya Toma, who has never forgotten what the Detective said, decides to become a detective. She returns to Japan after receiving training by the FBI in the United States. Saya Toma is assigned to work unsolved cases in the Public Security Bureau. Meanwhile, because of Satoshi Chii's (Yuu Shirota) scheme, Juichi Ninomae (Ryunosuke Kamiki) 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 (Umika Kawashima) becomes involved in their fight. To protect Maho Ueno, Saya Toma uses "spec".