In the sixth installment of Taisho Roman Tanteitan, Kai Todo, "the Japanese Sherlock Holmes," takes on a serial murder case.

Rikka Isurugi (Chihiro Yamamoto), head of the Fox Clan, is investigating the "White Lotus," a mysterious cult suspected of plotting a rebellion against the Shogunate. During her mission, she encounters Okyo (Kanon Miyahara), a Fuma Ninja dispatched by the Shogun. Their paths converge as they face a formidable common enemy: the Iga Ninja clan, led by Hattori Hanzo (Kane Kosugi), who harbors a deep vengeance against the Tokugawa family. A three-way conflict between the Fox Clan, Fuma Ninja, and Iga Ninja is about to begin.