Cross Academy is attended by two groups of students: the Day Class and the Night Class. At twilight, when the students of the Day Class return to their dorm, they cross paths with the Night Class on their way to school. Yuki Cross and Zero Kiryu are the Guardians of the school, protecting the Day Class from the Academy's dark secret: the Night Class is full of vampires!

Zero is suspected of killing Shizuka Hio, the pureblood vampire who murdered his family. Incensed, the vampire senate sends assassins to Cross Academy to execute him. Will the Night Class intervene, or will Kaname let Zero take the fall?