德川家齐的宠妾美代掌控大权的第十二代将军家庆的时代，为了解决继承权问题幕府与大奥之间的派阀开始进行斗争，为了揭露大奥中隐藏的政权争执和阴谋，阿缝潜入大奥当“间谍”，化身正义的伙伴。

After the sudden death of her adoptive father Shimada Mataemon, Nui, whose own father met an untimely death when he was about to expose the corruption of the shogunate becomes determined to expose the collusion between Kannouji, and the unforgivable relationships between the ladies in waiting of the inner palace and the monks. Nui is undertaking this undercover investigation without regard for the danger she is putting herself in, for the sake of Shinnosuke whom she secretly loves