The scenes of the story are laid in Japan during the last revolution in the late 1860s. The Emperor is growing old and infirm. He has two sons: Yorotomo, the elder, will succeed to the throne; his younger brother Togowawa would succeed to the throne in the event of his brother's death. The Emperor, for reasons of state, betroths Yorotomo to Sada San, daughter of the Prime Minister. The Chief Shogun, supposedly loyal to the emperor, covets the throne. He realizes that the Japanese people would never permit him to ascend the throne himself, and he casts about for a dummy to occupy it. The Shogun calls upon the younger prince and unfolds his plan to kill Yorotomo. Togowawa enters into the conspiracy and promises to aid the Shogun. The conspirators are overheard by a spy of the Emperor, who reports the plot. Yorotomo is sent away in disguise. During his sojourn he falls in love with Mimi San, daughter of the gardener of the summer cottage of the Mikado, who does not know that Yorotomo is a prince. The Mikado dies and Yorotomo is called to take the throne, and he is compelled to leave O Mimi San and marry Sada San.