The eighth shogun, Tokugawa Yoshimune, fights against evil rampant in Edo while blending in with the common people as Tokuda Shinnosuke, the third son of a poor samurai retainer, commonly known as "Shin-san". The story depicts Yoshimune, who is shaken by the issue of succession, the drama within Edo Castle, and a difficult case involving a conspiracy that occurs in the castle town, with the addition of new characters and a sense of the era.