Petrograd, Russia, at the turn of the twentieth century. Throughout Europe, a vampiric menace stalks the streets: Chiropterans, incredibly strong, inhuman monsters. A new organization of vampire hunters named Red Shield battles to stop the beasts, but they are outnumbered in the face of the superior might of the creatures. All that stands between the creatures and the end of humanity is a lone girl, Saya!
The novels explore the history of the Chiropteran menace, how Saya and her enigmatic mentor Hagi first met, and the inner secrets of the Red Shield organization.