In addition to being a private investigator, Shido Tatsuhiko is also a vampire who has no recollection of his past. Alongside Yayoi Matsunaga, a female agent of the government, Riho Yamazaki, his assistant and a teenage orphan, and Guni, a small green imp, Shido battles against evil creatures called Nightbreed. At the same time, Cain, the vampire responsible for his transformation, is on the hunt for him.