When the twins entered the common room, Bill was sitting at one of the tables on the edge of the room, doing his homework. "We need to talk to you," George said.

"But not here," Fred added. "To much of a risk of being overheard." He nudged George in the ribs and nodded towards one of the chairs by the fire, where Percy was attempting to train Scabbers to fetch gobstones.

Bill took a deep breath. "Look, I know you two are curious about Percy's love life, but it's really none of your business who he goes to Hogsmeade with and-"

George shushed him. "It's not about Percy, promise."

"Then-"

"It's sensitive," George said. He grabbed hold of Bill's hand and yanked him in the direction of boy's dorms. "Come on. Let's go up to..."

"Your room," Fred said. "It's more likely to be uninhabited."

Bill looked down at his half finished essay and then back up at the twins. "Do we have to do this now?"

"Yes," George said at the same time Fred said, "It could probably wait until morning."

George gave Fred a disgusted look.

"What? Bill can't do anything about it by himself. He'd need to talk to Dumbledore or McGonagall or somebody and he can't do that until tomorrow morning," Fred said. "At least, not without arousing a certain someone's suspicions. So if you want to finish that essay, we can just-"

"Oh, no," Bill said, in a voice that would brook no excuses. "I want to know what's going on."

"Brilliant." George tried to smile, but found himself too nervous to do more than grimace. "Let's go."

"Okay," Bill said, once he had managed to kick out two of his roommates. "We're alone in my room, no one can possibly be listening to us, so what is it that you two are worked up about?"

George gulped. Despite his certainty that Bill was the best person to go to, he found himself hesitating to say anything. What if Bill thought they were trying to pull a prank on him?

"Scabbers is actually a person," Fred said. "His name's Peter Pettigrew and we think-"

"Hold it," Bill said. "That is completely bonkers. And wasn't Peter Petttigrew that bloke you thought was going out with Percy?"

"We have proof," George said, "but we need you to promise not to confiscate it." He folded his arms in front of his chest, as though he really would refuse to tell Bill anything if he didn't promise.

Bill paused, evidently torn between wanting to know what this 'proof' was and his duty as Head Boy to uphold the rules of the school. "Fine. As long as your proof isn't dangerous, I won't confiscate it. But if Filch catches you with it-"

"He won't." Fred took the Map out of his pocket, touched his wand to the parchment, muttered "I solemnly swear that I am up to no good," as softly as he could, and found Gryffindor Tower. "Here," he pointed a finger at the common room as he thrust the Map into Bill's face. "There's Percy, by the fire, and Peter Pettigrew's with him."

Bill took the Map and ran his fingers over the dots in the common room. Then he looked over to one of the boys' dormitories, where a dot labeled George Weasley was pacing frantically. "You have a map of the school that shows where everyone is?"

"That's not the point," George snapped. "The point is that Scabbers is Peter Pettigrew."

"All right," Bill said. "That's rather strange, but Percy found Scabbers in the garden one day. Maybe his last owner-"

Fred shook his head. "We looked through everything. Percy found Scabbers in mid-November 1981, didn't he?"

"I'm surprised that you remember that," Bill said, before his eyes widened in realization. "You don't, do you? You're guessing, based on..."

"We found a bloke named Peter Pettigrew," Fred said. "Supposedly, he was killed on the first of November 1981, by Sirius Black-"

"I remember that," Bill said. "Sirius Black killed thirteen people with a single curse. It was all over the Daily Prophet, but Mum and Dad wouldn't talk about it."

"We looked through the records," George said, not mentioning that said records consisted of two newspaper articles. "And all they ever found of Pettigrew was a finger, same as Scabbers is missing. We talked through everything and it only makes sense if Pettigrew turned himself into a rat and ran off after blowing up the street-"

"You're making it sound like Peter Pettigrew was the one who cast the curse and killed all those muggles," Bill said, "but Sirius Black was the one selling secrets to You-Know-Who. Why would Pettigrew want to fake his death like that?"

"I hadn't thought about it," George admitted. "But-"

"How did they know that Black was the one leaking stuff?" Fred asked. "The Order of Merlin article took it for granted that Black was a Death Eater, likely You-Know-Who's second in command, but all the first article said was that Black was 'now known' to have been a spy and all they had to support it was what Pettigrew shouted at the scene."

Bill frowned. "I haven't ever studied this, but he came from a family of Death Eaters. His cousin-"

"That's not evidence," Fred said. "Didn't they say what he'd told You-Know-Who when he was tried?"

"He was an Auror," Bill said. "A lot of the things he leaked were probably top secret."

"But they wouldn't have still been top secret after the war," Fred said. "They would have been stuff like battle plans and when Ministry officials would have been vulnerable, wouldn't they? The kind of stuff that's only good for a couple of months at most."

"As an Auror he might have been more useful passing false information," George added. "Making sure that Death Eaters didn't get caught."

"This all might be true," Bill said, "but it's not going to convince anyone, especially not the Wizengamot, that Black isn't a Death Eater."

"It doesn't matter," George announced. Bill looked astonished and even Fred, who could generally be expected to be on level with George, looked confused. "From what the witnesses described Black couldn't have turned Pettigrew into a rat himself, so if Scabbers is Peter Pettigrew then Black is innocent of at least one of the murders he was convicted of." He glared a Bill and Fred, silently daring them to disagree.

"All right," Bill said. "I'll take this to McGonagall. If there's any way to tell if Scabbers is an animagus, she'll know it."