“Because . . . because people would know if Peter Pettigrew had been an Animagus. We did Animagi in class with Professor McGonagall. And I looked them up when I did my homework—the Ministry of Magic keeps tabs on witches and wizards who can become animals; there’s a register showing what animal they become, and their markings and things . . . and I went and looked Professor McGonagall up on the register, and there have been only seven Animagi this century, and Pettigrew’s name wasn’t on the list—”

Harry had barely had time to marvel inwardly at the effort Hermione put into her homework, when Lupin started to laugh. “Right again, Hermione!” he said. “But the Ministry never knew that there used to be three unregistered Animagi running around Hogwarts.”

“If you’re going to tell them the story, get a move on, Remus,” snarled Black, who was still watching Scabbers’s every desperate move. “I’ve waited twelve years, I’m not going to wait much longer.”

“All right . . . but you’ll need to help me, Sirius,” said Lupin, “I only know how it began . . . ”

Lupin broke off. There had been a loud creak behind him. The bedroom door had opened of its own accord. All five of them stared at it. Then Lupin strode toward it and looked out into the landing.

“No one there . . . ”

“This place is haunted!” said Ron.

“It’s not,” said Lupin, still looking at the door in a puzzled way. “The Shrieking Shack was never haunted . . . The screams and howls the villagers used to hear were made by me.”

He pushed his graying hair out of his eyes, thought for a moment, then said, “That’s where all of this starts—with my becoming a werewolf. None of this could have happened if I hadn’t been bitten . . . and if I hadn’t been so foolhardy . . . ”

He looked sober and tired. Ron started to interrupt, but Hermione said, “Shh!” She was watching Lupin very intently.

“I was a very small boy when I received the bite. My parents tried everything, but in those days there was no cure. The potion that Professor Snape has been making for me is a very recent discovery. It makes me safe, you see. As long as I take it in the week preceding the full moon, I keep my mind when I transform . . . I am able to curl up in my office, a harmless wolf, and wait for the moon to wane again.

“Before the Wolfsbane Potion was discovered, however, I became a fully fledged monster once a month. It seemed impossible that I would be able to come to Hogwarts. Other parents weren’t likely to want their children exposed to me.