The last princess of Japan's doomed Southern Court, Fujiwara Ryo has an offer she cannot refuse: a marriage proposal from her archenemy. As the shogun's royal prisoner, she'd live a comfortable life in a gilded cage. But Ryo isn't the kind of girl to take the easy way out, so refuse it she does. And now a failed revolt against the shogunate has put a price on her head and her spurned fiancé hot on her heels.

Ryo escapes with Sen, her loyal lady-in-waiting. Atop sacred Mt. Koya, Sen's uncle summons the mighty Kala Sarpa. If all goes as planned, the "Serpent of Time" will transport Ryo safely out of the shogun's reach. But Kala Sarpa bears a grudge of its own against the Fujiwara clan and seizes the chance to even the scales. Their fates fully entwined, Ryo must travel back to the past to save her future.