Just as Section 4 celebrates a coworker's transfer, they are assigned to reopen a cold case: the shooting of Sergeant Momose 12 years ago. The discovery of the murder weapon suggests a planned attack with an accomplice. When Takamine interviews the mother of the suspect, she learns that a detective had been in contact with her son before the murder. Section 4 now focuses its investigation on the detective to uncover his connection to the case.
