At the end of S volume 3, detective Masaki Shiiba was last seen running away from the hospital room of his injured S, Keigo Munechika. Now, Shiiba has turned in his resignation, bought a gun of his own, and is bent on only one mission—to kill Takanari Godou.

He vows to get the truth from Godou, even if he has to throw away his morals and life to do it. But can he do it? Can he shoot another person and commit cold-blooded murder for revenge?