People living in an ordinary city, students and teachers at a school, and police officers... they were living very peacefully. Just like innocent sheep who all get along well together in a flock. ... until they found out that murderer is hiding among students and teachers at school. In order to find out who the murderer is, they decide to stay at the school instead of returning home until the murderer is caught. They are friendly with each other, but at the same time they are suspicious of each other. The same goes for you, you have to spy on them, find evidence and find out who the murderer is. Besides, maybe there isn't just one murderer. or... maybe, You're murderer?