Ever since the Death Eaters went to war in Hogwarts and successfully drove away the nail called "Dumbledore's Army" left by the Order of the Phoenix, this ancient magic school has gradually been controlled by Snape. In particular, there was the case of the owner of the Pig Head Bar who was implicated by following the clues. The professors who originally had different ideas had to choose to stay dormant to avoid causing trouble for themselves and others.