If Percy Jackson and Co. were at Hogwarts this is what I imagine would happen in the Prisoner of Azkaban when Sirius drags Ron in the Shrieking Shack. I imagine this would be chapter 17 in the book.
People present: Harry, Ron, Hermione, Scabbers, Sirius, Remus, Snape, Percy, Annabeth, Jason, Piper, Frank, Hazel, Leo, Nico
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"Why should I listen to you?" Harry asked. "You murdered my parents!" Harry pointed his wand at Sirius.
"WAIT!" screamed Percy.
"What, why?" asked Hermione.
Percy turned to the wall with his wand outstretched. "Silencio, Petrificus Totalus, Expelliarmus!" A wand flew into his waiting hand. He put it in his pocket and walked to the wall. "I'll take that, thank you!" Percy said cheerily. He grabbed what seemed to be space and pulled.
"SNAPE!?" Everyone asked.
Indeed Snape was there.
"He was listening in so that he can take the wrong information back to school. After all, they won't listen to a bunch of third years. He probably found the cloak in the entrance of the Whomping Willow when we entered. Now say goodnight Snape." Percy said in the same cheery voice.
Percy uncapped Riptide. If Snape could run, he would've. But he couldn't. Percy bashed his head with the flat of his blade and Snape fell unconscious.
"I wanted to do that since the first day I met him." Percy said. "Now, Hominum Revelio." Percy turned to Harry. "Where were we?"
Lupin, who has stayed silent through the exchange, said "Harry was accusing Sirius of murder. Murder he didn't do."
"BUT HE DID DO IT!" Harry yelled, enraged once more. "He killed my parents!"
"I did not! Someone else did and he is in this room." Sirius croaked.
Ron suddenly said, "Scabbers stay still, will you?"
"THERE IS NO ONE HERE WHO WAS AT THE SCENE OF THE CRIME! AND PETTIGREW'S DEAD!"
"That's where you're mistaken." Nico said, calmly.
"WHAT!? BUT HE'S DEAD AND THE REASON FOR THAT IS RIGHT IN FRONT OF ME!"
Nico sighed. "Harry, I sense death, remember? I visited the Underworld while I am here and there is no Peter Pettigrew anywhere."
"THAT DOESN'T MATTER. BLACK KILLED MY PARENTS! HE SOLD THEM OVER TO VOLDEMORT!"
"Stop, Harry," said Percy, impossibly quiet. "I get it now." The dreams he had of Pettigrew's betrayal, the rat in Ron's hands with the missing toe, Lupin's three best friends becoming unregistered animagi for the full moon nights, Snape's hatred towards Lupin, it was all a big puzzle and he found the missing puzzle piece. Everything made sense to him. But no one knew what was happening in Percy's mind. After all, everyone underestimated him.
"WHAT DO YOU MEAN, YOU GET IT NOW?! SIRIUS BLACK IS A MURDERER."
"No," Percy said, still impossibly quiet. He stepped in front of Sirius Black.
"WHY ARE YOU DEFENDING HIM? WHY ARE YOU LISTENING TO HIM?"
"You want to know why Harry? Because in those eyes, I see myself. I see a broken man, broken from everything I had to do, yearning for revenge because of everything I went through, so close to it, but I can't. Why? Because I have to stay good for the sake of everyone else. The biggest difference between Black and I, is the fact that he can get revenge, and he will get it, but not with the bad way, murder. I'll take a good way, justice. You ask me why I listen to him. What have I done these 3 years here? I listened to the campers back home, I listened to the demigods here, I listened to you, Harry, Ron, and Hermione, when you needed me, and I helped everyone. I listened to Professor Lupin when I figured out he's a werewolf, and stayed with him in his office on full moon nights, to keep him company. Where do you think I go when you wake up and see my bed empty? The fact is, I listen to everyone because no one listens to me. I listen because even if no one helps me, I want to help everyone. So yes, I will listen to him, because everyone needs someone to listen to them. Even you, Pettigrew. Change back when you feel comfortable. I will listen and serve justice rightly, like I always do."
And for the first time, Percy let his mask down in front of his friends. Everyone saw his broken eyes. What were usually calm waves were now a raging storm.
Everyone was struck speechless. It was true.
How many times had Percy listened to Leo and helped him get over his depression and obsession with cutting himself?
How many times had Percy listened to Annabeth and helped her with her family problems?
How many times had Percy listened to Jason and helped him figure out where he belongs?
How many times had Percy listened to Piper and helped her with her fame struggles and saw her as a human being, not as the daughter of a famous actor?
How many times had Percy listened to Hazel and helped her get to know and fit in modern times?
How many times had Percy listened to Frank and helped him be comfortable with who he is?
How many times had Percy listened to Nico and helped him feel included where others ignored him?
How many times had Percy listened to Harry and helped him through his hard times?
How many times had Percy listened to Hermione and helped her with her work when he figured out about the time turner?
How many times had Percy listened to Ron and helped him with his work, boosted his self-esteem, and helped him practice for when he tried out for the Keeper position in Quidditch?
And did someone ever think that Percy had problems? Was there anyone who ever listened to Percy?
No, not a single soul. Not even Annabeth, his girlfriend.
"I'm so sorry, Percy." Annabeth started.
Percy put his mask back up. "Not now Annabeth." He cut her off. "Now is no time to listen to me. Now is the time to listen to Sirius and Professor Lupin. The full moon is tonight after all, and I don't want to be in here much longer.
So they listened.
"That's where all of this starts — with my becoming a werewolf. None of this could have happened if I hadn't been bitter... and if I hadn't been so foolhardy..."
He looked sober and tired. Leo started to interrupt, but Piper shushed him. 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'm 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.
"But then Dumbledore became Headmaster, and he was sympathetic. He said that as long as we took certain precautions, there was no reason I shouldn't come to school..." Lupin sighed and looked directly at Harry. "I told you, months ago, that the Whomping Willow was planted the year I came to Hogwarts. The truth is that it was planted because I came to Hogwarts. This house" — Lupin looked miserably around the room, — "the tunnel that leads to it — they were built for my use. Once a month, I was smuggled out of the castle, into this place, to transform. The tree was placed at the tunnel mouth to stop anyone coming across me while I was dangerous."
Everyone except Percy and Sirius couldn't see where this story was going, but they were listening raptly all the same. The only sound apart from Lupin's voice was Scabbers's frightened squeaking.
"My transformations in those days were — were terrible. It is very painful to turn into a werewolf. I was separated from humans to bite, so I bit and scratched myself instead. The villagers heard the noise and the screaming and thought they were hearing particularly violent spirits. Dumbledore encouraged the rumor... Even now, when the house has been silent for years, the villagers don't dare approach it...
"There are no actual spirits here. I feel nothing." Nico interrupted.
"But apart from my transformations, I was happier than I had ever been in my life. For the first time, I had friends, three great friends. Sirius Black... Peter Pettigrew... and, of course, your father, Harry — James Potter.
"Now, my three friends could hardly fail to notice that I disappeared once a month. I made up all sorts of stories. I told them my mother was ill, and that I had to go home to see her... I was terrified they would desert me the moment they found out what I was. But of course, they, like you, Hermione, Percy, worked out the truth...
"And they didn't desert me at all. Instead, they did something for me that would make my transformations not only bearable, but the best times of my life. They became Animagi."
"My dad too?" said Harry, astounded.
"Yes, indeed," said Lupin. "It took them the best part of three years to work out how to do it. Your father and Sirius here were the cleverest students in the school, and lucky they were because the Animagus transformation can go horribly wrong — one reason the Ministry keeps a close watch on those attempting to do it. Peter needed all the help he could get from James and Sirius. Finally, in our fifth year, they managed it. They could each turn into a different animal at will."
"But how did that help you?" said Jason, sounding puzzled.
"They couldn't keep me company as humans, so they kept me company as animals," said Lupin. "A werewolf is only a danger to people. They sneaked out of the castle every month under James's Invisibility Cloak. They transformed... Peter, as the smallest, could slip beneath the Willow's attacking branches and touch the knot that freezes it. They would then slip down the tunnel and join me. Under their influence, I became less dangerous. My body was still wolfish, but my mind seemed to become less so while I was with them."
"Hurry up, Remus," snarled Black, who was still watching Scabbers with a horrible sort of hunger on his face.
"I'm getting there, Sirius, I'm getting there... well, highly exciting possibilities were open to us now that we could all transform. Soon we were leaving the Shrieking Shack and roaming the school grounds and the village by night. Sirius and James transformed into such large animals, they were able to keep a werewolf in check. I doubt whether any Hogwarts students ever found out more about the Hogwarts grounds and Hogsmeade than we did... And that's how we came to write the Marauder's Map, and sign it with our nicknames. Sirius is Padfoot. Peter is Wormtail. James was Prongs."
"What sort of animal —?" Harry began, but Annabeth cut him off. "That was still really dangerous! Running around in the dark with a werewolf! What if you'd given the others the slip, and bitten somebody?"
"A thought that still haunts me," said Lupin heavily. "And there were near misses, many of them. We laughed about them afterward. We were young, thoughtless — carried away with our own cleverness.
"I sometimes felt guilty about betraying Dumbledore's trust, of course... he had admitted me to Hogwarts when no other headmaster would have done so, and he had no idea I was breaking the rules he had set down for my own and others' safety. He never knew I had led three fellow students into becoming Animagi illegally. But I always managed to forget my guilty feelings every time we sat down to plan our next month's adventure. And I haven't changed..."
Lupin's face had hardened, and there was self-disgust in his voice. "All this year, I have been battling with myself, wondering whether I should tell Dumbledore that Sirius was an Animagus. But I didn't do it. Why? Because I was too cowardly. It would have meant admitting that I'd betrayed his trust while I was at school, admitting that I'd led others along with me... and Dumbledore's trust has meant everything to me. He let me into Hogwarts as a boy, and he gave me a job when I have been shunned all my adult life, unable to find paid work because of what I am. And so I convinced myself that Sirius was getting into the school using dark arts he learned from Voldemort, that being an Animagus had nothing to do with it... so, in a way, Snape's been right about me all along."
He looked up at Harry, Ron, Hermione, and the demigods. "Professor Snape was at school with us. He fought very hard against my appointment to the Defense Against the Dark Arts job. He has been telling Dumbledore all year that I am not to be trusted. He has his reasons... you see, Sirius here played a trick on him which nearly killed him, a trick which involved me —"
Black made a derisive noise.
"It served him right," he sneered. "Sneaking around, trying to find out what we were up to...hoping he could get us expelled..."
"Severus was very interested in where I went every month." Lupin told them. "We were in the same year, you know, and we — er — didn't like each other very much. He especially disliked James. Jealous, I think, of James's talent on the Quidditch field...anyway Snape had seen me crossing the grounds with Madam Pomfrey one evening as she led me toward the Whomping Willow to transform. Sirius thought it would be — er — amusing, to tell Snape all he had to do was prod the knot on the tree trunk with a long stick, and he'd be able to get in after me. Well, of course, Snape tried it — if he'd got as far as this house, he'd have meta fully grown werewolf — but your father, who'd heard what Sirius had done, went after Snape and pulled him back, at great risk to his life... Snape glimpsed me, though, at the end of the tunnel. He was forbidden by Dumbledore to tell anybody, but from that time on he knew what I was..."
"So that's why Snape doesn't like you," said Frank slowly, "because he thought you were in on the joke?"
"That's right," said Percy.