There has been an outbreak of bizarre serial murders in which the victims get the blood from the entirety of their bodies extracted. The media created an uproar, calling it the work of "the vampiric wolves of the modern era, Vamwolf". Despite the chaos, Shirakawa Seri (the protagonist) leads a fun, peaceful life helping out at the apartment her father manages and interacting with its kind residents.
However, one day, Seri's father passed away, having become a victim of murder. Based on the modus operandi, it was conjectured that his murder was the doing of the rumoured "Vamwolf". After the funeral, as she went through the belongings left behind by her father, Seri found a memorandum and gun hidden in a secret compartment of his desk. Though she thought that her father was an apartment manager, the memorandum reveals a certain truth: he was in actuality a "Vamwolf Hunter", along with his "comrades (the residents of the apartment)".
On the last page, he had left only a single question behind:
"Is there a Vamwolf among my comrades who's tricking us?"
Is there a Vamwolf amidst the apartment's residents? Was Seri's father murdered by this Vamwolf?
Driven by her sole desire to learn the truth, she resolves to find the Vamwolf among her father's comrades.
[Translation of the official website's story summary.]