thought Sirius betrayed your parents, and Peter tracked him down -- but it was the other way around, don't you see? Peter betrayed your mother and father -- Sirius tracked Peter down --" 

"THAT'S NOT TRUE!" Harry yelled. "HE WAS THEIR SECRET-KEEPER! HE SAID SO BEFORE YOU TURNED UP. HE SAID HE KILLED THEM!" 

He was pointing at Black, who shook his head slowly; the sunken eyes were suddenly over bright. 

"Harry... I as good as killed them," he croaked. "I persuaded Lily and James to change to Peter at the last moment, persuaded them to use him as Secret-Keeper instead of me.... I'm to blame, I know it.... The night they died, I'd arranged to check on Peter, make sure he was still safe, but when I arrived at his hiding place, he'd gone. Yet there was no sign of a struggle. It didn't feel right. I was scared. I set out for your parents' house straight away. And when I saw their house, destroyed, and their bodies... I realized what Peter must've done... what I'd done...."

 His voice broke. He turned away. 

"Enough of this," said Lupin, and there was a steely note in his voice Harry had never heard before. "There's one certain way to prove what really happened. Ron, give me that rat."

 "What are you going to do with him if I give him to you?" Ron asked Lupin tensely. 

"Force him to show himself," said Lupin. "If he really is a rat, it won't hurt him." 

Ron hesitated. Then at long last, he held out Scabbers and Lupin took him. Scabbers began to squeak without stopping, twisting and turning, his tiny black eyes bulging in his head. "Ready, Sirius?" said Lupin. 

Black had already retrieved Snape's wand from the bed. He approached Lupin and the struggling rat, and his wet eyes suddenly seemed to be burning in his face.