The murder apparently occurred during the historical Great Fire of Meireki that destroyed much of Edo city and took the lives of many people in the confusion.

Meanwhile, the tension between Sano and Lord Matsudaira reaches a boiling point and they are on the verge of open warfare, a situation brought about by the manipulation of Yanagisawa Yoshiyasu who had earlier escaped from exile.

In the prologue, a Shinto priest passing by discovers remains of a human unearthed when strong winds toppled an oak tree near the Inari Shrine.

The shogun informs them that the skeleton of his long-lost cousin, Tokugawa Tadatoshi, who was thought to have perished during the Great Fire of Meireki, has been found and charges Sano with the investigation.

Sano is shocked that his mother is not a humble commoner as he had thought, but a scion of the Kumazawa clan, a respected hereditary Tokugawa vassal.