Sutematsu and Sukekichi, residents of Benten Nagaya tenement, witness a woman being thrown from a palanquin into a river and are immediately attacked by several samurai. They are saved by a fellow tenant, the ronin Ginzaburo Fujizaki. One of the assailants drops a wooden tag bearing the Onitsuta-bishi (demon ivy diamond) crest. The next morning, the woman’s body is found on the lumber dock. She is Omino, daughter of Omiya, a money exchanger in Nihonbashi.