AN: This was written for the QLF Competition, with the prompt that on the night of Pettigrew's escape, Lupin bit a student. I swear the organisers of QLFC are doing everything in their power to force us to write angst. Game on.

In canon, it was never explained why the elaborate time loop happened at all, rather than the natural course of events (i.e. the Dementors Kiss them all, The End). I have an elaborate head canon of time travel which I've been developing in the hopes of use in a tabletop role-playing game, which needs to be able to support six or so idiots trying to paradox one another out of existence; the percept sequence theory is a very heavily restricted version of that. It has mechanics I haven't explained for interleaved jumps which could justify the time loop, but … it's complicated.

… … …

"You explain," said Harry, helping himself to more chocolate.

Hermione, her voice low, began filling Ron in on her Time-Turner, and how they'd gone back and rescued Buckbeak and Sirius. His eyebrows slowly climbed toward his hairline.

"You can go back in time," he said.

"Yes," said Hermione.

"In time," he emphasised.

"Yes, we've established –"

"And you've been using it to overload your courses?"

Hermione opened her mouth to deliver a scathing retort, but at that moment, there came a jangling at the door. It opened a moment later: in came a girl Harry vaguely recognised as Kelly something, the Hufflepuff prefect. Leaning against her were the Weasley twins, covered in blood and leaning against her heavily. Harry sprang out of his bed and caught at Fred as he swayed and began falling to the floor.

"What –?" he asked.

"They've been bitten," Kelly said.

Madame Pomfrey took George's other arm and, with Kelly's help, led him to a bed and lifted him in. "Get them horizontal."

Ron tried to sit up to help, and gave a gasp of pain as he moved his damaged leg. Hermione was at Harry's side in a moment and helped him lift Fred into his own bed.

"Bitten?" said Hermione. "What by?"

Madam Pomfrey eased Fred's mangled shirt up and ran her wand over his chest. He stirred and moaned.

"Burns," he whispered.

"He's feverish," said Madam Pomfrey. "It's a full moon … oh, dear …"

Harry, Hermione and Ron exchanged looks of horror. Professor Lupin …

"Madam Pomfrey?" Harry asked. He held up his hands, which were streaked with blood. "We should wash our hands."

"Yes, yes," said Madam Pomfrey distractedly, waving them toward the ward's bathroom. Kelly stayed with her, helping loosen the twins' clothing.

The bathroom had two toilets in stalls and a sink. One of the stall doors was locked. Hermione turned on the tap and they stuck their hands under. "Oh my gosh," she said. "They've been infected … this is horrible …"

"Hermione," he said in a very low, very urgent voice. "We have to help them."

"There's no cure," she said. "There's nothing we can do."

"Yes, there is," said Harry. He slipped a finger under her neckline and drew out the Time-Turner.

She stared at him. "What? No. No no no, we can't. If you change the past, terrible things will happen. Professor McGonagall –"

"More terrible than becoming werewolves?" he asked.

"Harry, it's not that I wouldn't, it's that I can't. If you change the past, a paradox forms, and it usually gets resolved by whoever's time travelling being killed. And they usually don't even manage what they set out to achieve."

"That's rubbish," Harry whispered back. "We just changed the past by rescuing Sirius and Buckbeak."

Hermione sighed. "Okay. The rule is that you form a paradox if you change what's called your own percept sequence. We never changed anything about what our past selves saw, except you casting that Patronus. I have no idea how that worked."

"Well, it makes sense, doesn't it?" said Harry. "I could cast it, because I already saw myself –"

"It makes no sense at all!" Hermione hissed back. "We should all have been Kissed! Self-proving time loops don't happen. Someone has to decide to go back."

"Dumbledore?" suggested Harry. "He wouldn't have wanted us to be Kissed. He could have used Polyjuice, and taken the Time-Turner …"

Hermione frowned and sketched a non-orientable circle in mid-air. She winced. "I really, really hate interleaved percept sequences. Let's not overthink it or we'll be here all night. Anyway, we can't stop them from getting bitten, or we'll change our own percept sequences."

"What if we make something else bite them instead?" said Harry.

"If our future selves have already done that," said Hermione, "we'll need to have done it in such a way that we as of five minutes ago would have still thought it was Professor Lupin. They were definitely bitten by a large animal, and Fred was burning up … where are we going to get a large animal from at short notice?"

Harry locked eyes with her.

"No," she said, "no, no this is a terrible –"

Harry pulled her Time-Turner over his head and spun it once.

Ten past eleven p.m.

Harry and Hermione staggered and bounced off the wall.

"– idea," said Hermione.

"We have to try," said Harry, shucking the necklace. "Come on."

They tiptoed out of the empty ward. They passed a window; down in the grounds they could see black Dementor silhouettes against the silvery light of past-Harry's Patronus, and they could just about make out their further-past selves lying on the ground.

"We still can't let us see us, can we?" asked Harry.

"Absolutely not," said Hermione. "Well, we can see past us, but not vice versa. Come on, we only have a few minutes' head start."

They set off for the nearest staircase. "Does it matter?" Harry asked. "We could just go back another hour …"

"The chances of a paradox go up exponentially with each concurrent loop," Hermione said in her reciting-from-a-book voice.

They had to duck behind the plinth of a statue of Melvin the Morose to avoid a patrolling Percy, and a tapestry when some ghosts passed, and it took them exactly nine minutes to get to Professor Flitwick's office. An alohamora later, and they were inside. Hermione led Harry to a wardrobe, which for some reason contained about thirty silk negligees, and shut the door behind him.

It was only two minutes more before they heard footsteps and voices.

"– taking him?" asked Percy. "Surely the dungeons would –"

"The dungeons are riddled with secret passages, which Black knows better than anyone," came Snape's voice. There came the sound of a door opening, a thump, and the door closing. "Colloportus. Stay here, Weasley, and guard this door with your life. Do not let anyone through but myself, the Minister, his executioner or the Dementors."

"Yes, sir," said Percy. The footsteps began retreating. Harry waited until they had faded away altogether before lighting his wand and opening the door.

The office was always cluttered. Books lay haphazardly across the floor; there were two real palm trees framing the window; and a toddler-sized desk in the middle, covered in partially-marked exams. Sirius Black lay against the desk, rubbing his head.

"Merlin, but ow," he said.

"Sirius!" whispered Harry.

Sirius looked up. His eyes widened. Harry put his finger to his lips and pointed to the door.

"What are you doing here?" Sirius whispered. "Why didn't they take your wand?"

"We're from four hours in the future," Harry replied.

"…" said Sirius.

"We need you to escape and bite the Weasley twins so they don't become werewolves," Harry explained.

Sirius rubbed his head again.

"Wait," said Hermione, "Fred said his wound was burning, we can't just have him be bitten."

"Maybe we could hit him with a fire charm?" Harry suggested. "It's still better than becoming a werewolf."

"That won't work," said Hermione, "Madam Pomfrey will notice and say something if we do that. It'd have to be something with similar symptoms to infection."

"Which are?"

"Red and inflamed skin," she recited effortlessly, "high temperatures, pain …"

"Are there any charms that do that?" Harry asked. "Or plants? Potions? Anything?"

Hermione screwed up her face in concentration. "Leocrottic Acid? But that isn't used in Potions until NEWT year. We'd have to break into Snape's stores …"

"Not a problem," Harry whispered back. "He wasn't in there an hour ago, was he?"

Hermione ran her hands through her hair. "I really, really don't like this."

"What's going on?" Sirius asked.

Hermione pulled her Time-Turner back out and slipped it over their necks. It was a rather tight fit, but she just managed. She gave it a flick.

Twenty-five minutes past ten p.m.

"Is anyone around here right now?" Harry asked at normal volume, ducking out of the Time-Turner.

"I don't think so," said Hermione. "Professor Flitwick sleeps in Ravenclaw Tower; there's nothing interesting here yet."

"Er," said Sirius.

"Right," she said. "Sirius, you'll have to wait in the Forest; we absolutely can't let anyone see you. Harry and I will find some Leocrottic Acid and meet up with you later. I think our past selves will be in the Forest, too, but you mustn't let them see you; stay in dog form and only approach the us with a bottle of Leocrottic Acid. We'll keep it open so you can smell it."

"I don't understand this at all," he said.

"Just go!" said Harry.

"And make sure nobody sees you!"

Sirius shrugged, morphed into the shaggy black dog, and loped off down the corridor.

Harry had spent enough time with the Marauder's Map to remember quite a few secret passages, and they made it down to the dungeons without meeting anyone.

"Stand guard; I know his filing system better," Hermione whispered. "Alohamora!"

When she returned a minute later, Harry was backed against a wall, trying not to look guilty as Kelly the prefect gave him a questioning look.

"Oh, hello," said Hermione, trying not to look as though she was holding a jar freshly stolen from a teacher's supplies.

"What are you doing here?" asked Kelly, as though it weren't obvious.

"This is medicine," Hermione said, "for Professor Lupin. Professor Snape brews it for him, but he's busy tonight, out on the grounds, so he asked us to deliver it for him."

Kelly raised an eyebrow. "Why wouldn't he ask a Slytherin?"

"He has this idea that we're busy breaking school rules every time his back is turned," said Harry. "He keeps giving us busywork like this, to distract us. It's starting to get annoying."

Kelly looked at them for a moment longer.

"Alright," she said, "carry on."

Hermione diligently locked the door behind them, and they set off down a corridor which led toward Professor Lupin's office, past a window on the first floor which Filch hadn't boarded up properly.

"Thank Merlin for Hufflepuffs," Harry said, as he prised the boarding off.

"Harry, we were seen," Hermione said, beginning to hyperventilate. "We were seen! What will we do? She's going to check with Snape, and when he hears that we were at his office when right now we're also with him in the Shack –"

"Hermione, calm down and let me think," he said. "Look, we haven't been paradoxed out of existence yet, so it isn't –"

"That's because the paradox wave hasn't completed a cycle yet," Hermione said distractedly. "They travel forward at the speed of time, and –"

"Okay, okay." Harry ran his hands through his hair. "Look, we'll just have to make sure she never tells him."

Hermione stared at him. "We are not murdering a prefect! Nor are we abducting her, modifying her memory, or –"

He raised his eyebrows. "I meant that in the morning, we should ask Professor Lupin to tell her that we took him his potion," he said.

"Oh," she said.

"But, if you feel like that wouldn't be thorough enough …"

"Oh, shut up and help me down," Hermione said.

They dropped out of the window and onto the grounds, where they headed into the Forbidden Forest, keeping low.

"We're already in there, aren't we," Harry said.

"Yes," said Hermione, checking her watch. "And in the Shrieking Shack, and we'll be in the Hospital Wing bathroom in a moment, too. Let's not forget the two Siriuses, either."

They went a few dozen yards into the Forest and sat down. Hermione unscrewed the lid of the jar. "Let's take stock," she said. "We need Sirius to find us, find the twins, bite them, and then get back to Flitwick's office so we could rescue him on Buckbeak, while we get back to the Hospital Wing." She frowned. "He can't get back before he left, or he'll self-interact. But that means we'll need to go through Percy."

"Maybe Sirius knows a jinx that'll knock him out for a minute?" Harry suggested.

Appropriately enough, Sirius chose that moment to lope up and transform back into a human.

"You two are the ones from the right timeline, right?" he asked.

"Yes," said Hermione. "Unless we Turn again, but … ugh, let's hope it doesn't come to that. Do you know where the twins are?"

"I could smell two people who smelt very similar to each other, and to your friend Ron," said Sirius. "They're about three hundred yards away, inside the Forest."

"What are they even doing out here?" Hermione asked. "They're missing the exams after-party; why would they rather wander around the Forbidden Forest at night?"

"There are some things you'll never understand, Hermione," said Harry.

"Clearly," she said. "Moving along, here's my idea. Harry and I will hang back. Sirius will transform and savage them. It has to look enough like a werewolf attack to fool Madam Pomfrey for at least a few minutes. You'll then have to spatter them with the Acid. Don't worry, it's not too strong, it won't kill them."

"Why am I doing this again?" asked Sirius.

"Because if you don't, they'll become werewolves," she said, handing over the jar. There came the sound of her shrieking from the grounds. "Go, now! I screamed right after Professor Lupin transformed!"

"Okay, sure, fine," said Sirius. He took the jar of Acid, screwed the lid back on, transformed back into dog form, and vanished into the woods.

"Hey, Hermione," said Harry. He yawned. "What about Lupin?"

"Hm?"

"What's to stop him from biting them, too?"

There was a beat, and they both took off after Sirius.

They found him standing over the badly mauled Weasley twins, sprinkling the Acid over their wounds.

"Ew," said Harry.

"You told me to make it convincing," Sirius said with a shrug.

A moment later, he was in dog form, squaring off against a fully-grown werewolf, but Lupin wasn't interested in a fight; he ran off deeper into the Forest. After a minute, Sirius transformed back again.

"Oh," said Hermione, "Professor Lupin was tired because he'd just fought you already."

"He won't be back tonight," said Sirius. "He never fought me and James over the same thing twice in one night."

"So they'll be fine," said Harry, of the twins. "Well, after Madam Pomfrey fixes them up."

There came an ambient silvery glow, as of the light of a powerful Patronus reflecting off the castle.

"That's it," said Hermione. "We need to get back to Flitwick's office now."

"Uh, why do I have to go back?" asked Sirius.

"Something about a paradox and killing us all," Harry replied. "Don't worry, we break you out again in" he checked his watch "about twenty minutes." He blinked. "We only have twenty minutes to break you back in! Come on, hurry!"

Unfortunately, every teacher and ghost in the school had seen the Patronus light, and were congregated at the front gate. Harry, Hermione and Sirius dithered for a minute, before Hermione suggested they levitate one another back through the window they'd used to exit. They climbed up, then slipped through one secret passage after another, dodging Filch and Peeves, who was still laughing at Sirius' imminent Kissing.

"I kind of miss old Peevesy," he said, showing them a passage hidden behind a pot plant. "He really would have brightened Azkaban up."

"Five minutes," said Hermione anxiously.

Three and a half minutes later, they reached Flitwick's office. Percy was still standing guard.

"Hi! Who goes there?" he challenged.

Sirius held his hand out to Harry, who wordlessly passed him his wand. "Confundo. Alohamora." He opened the door. "Ooh, obliviate, too. I still don't get what's going on. Why am I –"

"Expelliarmus," said Hermione. Sirius was blasted into the office; Harry caught his wand and slammed the door. "Colloportus. Finite." She turned this last on Percy; they ran for it before his wits fully returned to him.

They stopped up short just outside the Hospital Wing. Kelly was outside, eavesdropping against the door's keyhole. There was no way to get in without her noticing.

Harry backed up a corridor, so she wouldn't see, and drew his wand. "Expecto patronum." A perfect white stag issued from its tip. "Find Madam Pomfrey and tell her there are two students in the Forbidden Forest who've just been bitten by a werewolf. Can you try to throw your voice when you say it, don't let her know I'm the one who sent you?"

The Patronus nodded, then ran back up the corridor; they heard Kelly squeak in surprise. They hid behind a statue; a minute later, Kelly rushed past with Madam Pomfrey.

They went into the Hospital Wing; they and Ron were lying unconscious in the beds.

"Okay, now this is the weirdest thing we've ever done," said Harry.

"Come on," said Hermione. She took him into the bathroom, into one stall, and locked the door.

Five minutes later, Dumbledore arrived with Madam Pomfrey, then Snape and Fudge, and then Kelly with Fred and George. A minute after that, their past selves entered the bathroom and began talking.

"Where are we going to get a large animal from at short notice?" asked Hermione. "No, no, no this is a terrible –"

Harry unlocked the stall door, and they went back into the ward, where Madam Pomfrey and Kelly were rubbing coagulants into the twins' bodies. Ron was sitting up in bed, looking crushed.

"Fred and George," he murmured. "You mean they're …"

Hermione walked up to him and whispered in his ear. "I wouldn't worry about it," she said.

"What? How can you say that? Don't you know what – why are you smiling?"

Hermione walked primly over to her bed and picked up a big block of chocolate.

"Your turn to explain," she told Harry.