"Incarcerous." Before Pettigrew could move, Snape had him bound in chains.
"Severus, please," said Pettigrew in a quavering voice. "You don't have to chain me! HE'S the criminal! Sirius Black is the murderer, not me!"
"Perhaps," said Snape. "And yet, he has not spent the last thirteen years living as a rat. Something curious is going on, and I intend to discover exactly what it is." Snape folded his arms and gave Pettigrew a withering glare. It was an awful look that demanded compliance, more powerful than any glare that Snape would give to the worse misbehavior of a Gryffindor. "Explain yourself," Snape demanded. "Now."
"I was scared," Pettigrew blubbered. "Black hunted me down! He had come to murder me, thirteen years ago, and I was certain that he would find me again! I hid because I was scared!" Pettigrew began sobbing. "Please, you have to understand…"
Snape leaned forward and narrowed his eyes. "I find it odd that you would hide from a wizard imprisoned in Azkaban," he said. "Why hide for the last thirteen years when no wizard has ever escaped?"
"But I was right to hide," Pettigrew said. "Black escaped, he did! Surely it was through the awful powers given to him by the Dark Lord!"
The expression on Snape's face changed subtly, as if he had made some sort of discovery. Harry wondered briefly what it was, but he was distracted when Black began shouting.
"Me? Get powers from You-Know-Who? You lying sack of-"
"Silencio." Snape casually silenced Black. "I am conducting an investigation."
Black scowled and attempted to say something nasty, but no words left his mouth.
Harry turned back to Pettigrew, and was struck by a memory from earlier in the summer. "Professor, Pettigrew said that Black hunted him down, but that wasn't how it happened. Mrs. Malfoy told me that Pettigrew was the one who chased after Black, trying to get revenge for my parents."
Pettigrew began to stammer. "I- but- that's not… I mean… Sirius was the Secret Keeper! He betrayed James and Lily to the Dark Lord!"
"Silencio." Pettigrew fell silent, and Harry saw that Snape was scowling once more.
"That's actually a good point," Harry said. Things were getting entirely too confusing.
"I think I can explain that," Lupin said, his voice sad. "When Harry's parents went into hiding, Dumbledore suspected that Voldemort had managed to place a spy in our midst. James did not hide the fact that he had chosen Sirius as his Secret Keeper, which meant that the spy would have known, as well. But if James and Lily changed their Secret Keeper at the last moment, without telling the rest of the Order, they would have remained protected while the spy would have been revealed."
"But why would they do that?" Harry asked. "And why wouldn't they choose you?"
"Because they must have suspected that I was the spy." Lupin's shoulder slumped.
Black rattled his chains, trying to get Lupin's attention. I'm sorry, he mouthed.
"For the last thirteen years I thought that you had betrayed James and Lily," Lupin said. "I'm the one who owes you an apology."
"Your tearful reunion will have to wait," Snape said sarcastically. "We are going to speak with the Headmaster. Lupin, bind Weasley's leg. Granger, you will transport Weasley back to the castle and take him to the hospital wing; mobilcorpus is the incantation. Lupin, you will guard Black, and I will guard Pettigrew."
Lupin nodded, and waved his wand at Ron. "Ferula," he incanted. Bandages burst from the tip and wrapped Ron's leg tightly, holding it in place so that the fracture would not be compounded when Ron was moved. Lupin then moved across the room toward Black.
"Everything is making so much sense," Hermione said as she walked toward Ron. "Black was trying to get into Gryffindor tower all year, because that's where Ron was with Scabbers. It wasn't a mistake, after all."
Harry could see that Hermione was proud of her deduction. She glanced toward Lupin, looking for some signal of approval from one of her favorite teachers. As she looked toward Lupin, she passed by Pettigrew. Harry saw her mistake too late.
"Hermione, look out!"
Pettigrew lurched to the side, falling into Hermione's legs. The young witch stumbled, and in a blink Pettigrew transformed himself into a rat. The shackles binding his body fell to the floor, far too large to restrain a rodent. Pettigrew nipped at Hermione's ankle with his yellow incisors, and Hermione dropped her wand with the shock of the sudden pain. Pettigrew was suddenly human again, grabbing Hermione's wand out of the air.
Harry raised his wand, but hesitated. He couldn't curse Pettigrew without taking a chance of striking Hermione. Snape, however, was less concerned.
"Stupefy!" Snape shouted. A bright light flew out of his wand, straight at Pettigrew, but Pettigrew dragged Hermione's body in front of him. Hermione was struck directly in the chest by Snape's petrifying charm.
Still using Hermione as a shield, Pettigrew lashed out with a curse of his own. "Confringo!"
The blasting curse missed Snape but struck the boarded window behind him, detonating with enormous force. Lupin and Snape were blown off their feet, and Black was blasted aside. Snape struck his head against the corner of wardrobe and felt to the floor unconscious, while Black was tumbling across the floor. Lupin landed squarely in the middle of the room, where the light of the full moon poured in through the now-open window. The moonlight struck Lupin squarely on the chest, and it was only a moment before he began to howl in pain. Harry could see that Lupin's body was already beginning to twist and transform.
"What are you going to do, Harry?" Pettigrew asked. Something about the animagus transformation had broken Snape's silencing charm. "In about thirty seconds you're going to have a furry little problem on your hands." As he spoke, Pettigrew inched toward the window, dragging Hermione's unconscious body toward the window, keeping her between himself and Harry.
Harry glanced around. Snape was unconscious, Lupin was transforming, and Harry had never given Ron back his wand. Black was not only wandless but also in chains. There was no way to save everybody from the werewolf and stop Pettigrew at the same time.
"Too late, Harry." As Pettigrew spoke, the werewolf that was Remus Lupin reared up and howled. The werewolf took a tentative step forward, still uncertain in its freshly transformed body, inadvertently interposing himself between Harry and Pettigrew.
Pettigrew recognized his opportunity and made his escape. He released Hermione and leaped at the open window, transforming as he flew through the air, his body twisting upon itself. A moment later, a small rat scuttled away into the night.
The werewolf looked around the cabin, moving its gaze back and forth between Harry and Hermione's petrified form. The werewolf was clearly becoming more comfortable in its body; its movements were smoother, and Harry could see the predatory gleam in its eye. It seemed as the werewolf was deciding who it wanted to eat first.
"Professor Lupin?" Harry asked tentatively. "You took your Wolfsbane Potion tonight… right?"
The werewolf's lip drew back, exposing its fangs. It began to grown, and an enormous glob of saliva dripped toward the floor. Harry took a step backwards, and the werewolf began to flex its hands, opening and closing them, reminding itself of the motion it would use to disembowel its victims.
Harry thought back to his classroom report. There were two chief methods of surviving a werewolf attack: running, and blowing the werewolf to pieces. Running was not an option; there were four helpless people in the Shrieking Shack, and Harry couldn't abandon them. That meant that Harry's only option was to blow the werewolf to pieces… but somewhere inside that werewolf was Remus Lupin, one of his father's dearest friends and one of Harry's favorite teachers.
Behind Harry, there was a clatter of chains, and then a low growling noise. A large black dog leapt out from behind Harry, barking raucously. The werewolf began to growl, and the dog growled back. The two canines began to circle one another, slowly. When the werewolf had moved several steps away from Hermione, the dog dove at the werewolf. The wolf and the dog became tangled up, barking and snarling and snapping at one another, tumbling across the floor.
Harry dashed past the fight and crouched down by Hermione. "Rennervate." After last year's fiasco outside the Chamber of Secrets, Harry had made sure to learn how to un-stun somebody. Harry thrust Ron's wand into Hermione's hands. "You get Ron, and I'll get Snape." Harry turned toward his teacher. "Mobilcorpus!"
Snape's body lifted into the air, and Harry quickly moved his professor out of the bedroom. As Harry moved, he felt Hermione's cat dash past his legs, headed for the secret passage. Behind Harry, Hermione followed with Ron. Once they were both outside of the bedroom, Harry turned back.
"Black! Let's go!"
The large dog disengaged from the werewolf and sprinted toward the door. As soon as the dog passed, Harry slammed the door shut, bracing it with his shoulder. A moment later the werewolf plowed into the door with enormous force, driving Harry backward several inches. Harry pushed back, but he couldn't fight a fully grown werewolf. The door began to creep open, inch by inch.
Suddenly, there was another body beside him. Sirius Black, once again in human form, was pushing against the door. Together, Harry and Sirius were able to reach a stalemate with the werewolf; the beast couldn't open the door any further, but Harry and Sirius were unable to force it closed.
Behind Harry, Hermione had levitated Ron out of the shack and into the secret passage. She returned for Snape.
"Hurry, Hermione!" said Harry. "We can't hold him forever."
"Almost there," Hermione called from the other room.
There was a loud rumbling sound from outside the shack, followed by a great explosion. The entire shack shook from the power of the blast. Surprised, the werewolf jumped back from the door; Harry and Sirius took the opportunity to slam the door completely closed. While Black held the door shut, Harry cast a locking charm. "Colloportus."
"Let's go," said Black, ushering Harry ahead of him. "That won't hold Remus for long."
As Harry and Black climbed into the trap door, they heard the door to the bedroom break open with a crash. Black pulled the trap door shut and drew the massive steel bar through the rings.
"There's no way for him to get through that," Sirius said. "He'd need opposable thumbs, first." Black looked down. Harry and Hermione stood on the floor of the passage. Slightly further on, Ron lay next to the still-unconscious Severus Snape.
"Well," said Black, looking from person to person. "That certainly got buggered up, didn't it?"
A/N: Thanks for the recommendations of Slytherin!Harry fics. A few of them I have already read - "On the Way to Greatness," by mira mirth, was suggested and is one of my favorites. Hope that gets finished. Also mentioned was "What Would Slytherin Harry Do," by Big D on a Diet. Just read that today, and it's hilarious. I read "They Shook Hands" by Dethryl once upon a time, and stopped for some reason. I'll have to go back and see what happened.
Haven't gotten around to the rest, but that doesn't mean I won't. And please, keep the suggestions coming. I love a good Slytherin!Harry story.