Samon Kamiyama, a yoriki of the Minami-machi magistrate infiltrates the Denzū-machi prison disguised as Mushuku Sahēji. Samon is mistaken for a snitch and about to be beaten up when he was saved by the quick thinking of a ferryman Sanji. The infiltration is the plan of Samon and chief elder Abe Isenokami, who has asked Samon to obtain smuggling evidence against shipping whole retailers Kawachiya Senemon and his son Sennosuke.