recently there's been some killings around hogwarts, and no one knew who it was, so they cancelled quidditch and a classes, because it was so dangerous they told everyone to stay inside their dorms with the doors locked for their safety, however, you had some different ideas, you wanted to go out and figure out who was doing this. Since the night you went out to investigate, they've been after you, phone calls of unknown numbers, writing in blood in walls and mirrors, ect. You don't know who they are, but you know how many there are, you have some evidence that you ran into them, ripping off one of the killer's mask, it was a ghost face mask.