Zen Seizaki, a public prosecutor at the Tokyo District Public Prosecutors Office, is investigating an instance of unethical medical experimentation involving a pharmaceutical company and a university. While conducting his inquiry, he stumbles upon a document compiled by anesthesiologist Shin Inaba, which includes blood samples mixed with human hair and skin, as well as a letter "F." As he digs deeper into the case, Seizaki discovers a secretive plot tied to a major election and a particular person in charge of the operation.