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.
Detective Tomo Yashiro is ordered to transfer to the Sixth Special Investigations Unit. it is in charge of deciphering documents of unsolved cases she begins work in her new post along with a senior detective Risa Narum who is called the expert of document deciphering for her unusual ability to predict the personality and thoughts of a writer from writings
Yu Takanashi, a former surgeon, joins the Comprehensive Diagnosis Department at Tenikai General Hospital, where he works alongside the brilliant yet eccentric Takao Ameku to solve mysterious medical cases.
