Prologue
The bite of the werewolf, Fenrir Greyback, had dire consequences. It didn't transform the young Remus Lupin. It killed him.
Sirius Black, James Potter, and Peter Pettigrew never became the Marauders. Without Remus Lupin to unite them, although they were still friends, the group never formed, the map was never made, and they never became Animagi. Why would they? After all, they had no werewolf that they had to accompany as animals. And after Peter Pettigrew betrayed the Potters, Sirius Black succeeded in killing him before the Aurors arrived.
The Shrieking Shack never was made for Remus Lupin. Dumbledore never planted the Whomping Willow. The Weasleys' car never crashed into the bloodthirsty tree. The car never went into the Forbidden Forest. And the car never saved Harry Potter and Ron Weasley from the acromantula, Aragog. Aragog and his children fulfilled Ron's greatest fear as they ate them.
On April 12, 1993, a decision was made. An important decision. Everyone was terrified. The Heir of Slytherin and the Monster he controlled were Petrifying hundreds of Muggleborns. Albus Dumbledore was gone, removed from office by Lucius Malfoy's threats. Ginny Weasley was captured in the Chamber of Secrets and everyone assumed her to be dead. Harry and Ron were dead. Now Deputy Headmistress Minerva McGonagall had no choice in what was to happen.
She had to shut down the school.