“Expelliarmus!” he yelled—except that his wasn’t the only voice that shouted. There was a blast that made the door rattle on its hinges; Snape was lifted off his feet and slammed into the wall, then slid down it to the floor, a trickle of blood oozing from under his hair. He had been knocked out.

Harry looked around. Both Ron and Hermione had tried to disarm Snape at exactly the same moment. Snape’s wand soared in a high arc and landed on the bed next to Crookshanks.

“You shouldn’t have done that,” said Black, looking at Harry. “You should have left him to me . . . ”

Harry avoided Black’s eyes. He wasn’t sure, even now, that he’d done the right thing.

“We attacked a teacher . . . We attacked a teacher . . . ,” Hermione whimpered, staring at the lifeless Snape with frightened eyes. “Oh, we’re going to be in so much trouble—”

Lupin was struggling against his bonds. Black bent down quickly and untied him. Lupin straightened up, rubbing his arms where the ropes had cut into them.

“Thank you, Harry,” he said.

“I’m still not saying I believe you,” he told Lupin.

“Then it’s time we offered you some proof,” said Lupin. “You, boy—give me Peter, please. Now.”

Ron clutched Scabbers closer to his chest.

“Come off it,” he said weakly. “Are you trying to say he broke out of Azkaban just to get his hands on Scabbers? I mean . . . ” He looked up at Harry and Hermione for support, “Okay, say Pettigrew could turn into a rat—there are millions of rats—how’s he supposed to know which one he’s after if he was locked up in Azkaban?”

“You know, Sirius, that’s a fair question,” said Lupin, turning to Black and frowning slightly. “How did you find out where he was?”

Black put one of his clawlike hands inside his robes and took out a crumpled piece of paper, which he smoothed flat and held out to show the others.

It was the photograph of Ron and his family that had appeared in the Daily Prophet the previous summer, and there, on Ron’s shoulder, was Scabbers.

“How did you get this?” Lupin asked Black, thunderstruck.

“Fudge,” said Black. “When he came to inspect Azkaban last year, he gave me his paper. And there was Peter, on the front page . . . on this boy’s shoulder . . . I knew him at once . . . how many times had I seen him transform? And the caption said the boy would be going back to Hogwarts . . . to where Harry was . . . ”

“My God,” said Lupin softly, staring from Scabbers to the picture in the paper and back again. “His front paw . . . ”

“What about it?” said Ron defiantly.

“He’s got a toe missing,” said Black.

“Of course,” Lupin breathed. “So simple . . . so brilliant . . . he cut it off himself?”