A historical mystery set at Osaka Castle during the celebration of Toyotomi Hideyoshi's son Hiroi's first birthday. Maeda Gen'i, Ishida Mitsunari, Kimura Shigenari, and Ishikawa Goemon become entangled in a plot surrounding an attempt on the Taiko's life and a struggle for power.

A celebration for the Taiko's son Hiroi's first birthday was held at Osaka Castle.