It was Sirius' birthday on 3rd November. Most of Gryffindor tower were excited as it drew near, because they had planned a huge upset.

Remus had overheard one day that Professors Dumbledore and McGonagall were leaving for the weekend. When he told this to James and Sirius, they wasted no time in recruiting most of the boys of Gryffindor—including some of Prefects like Fabian Prewett into their plan.

In the evening of Sirius' birthday, they saw a group of unsuspecting Slytherins entering the library. The Gryffindor army except Remus followed, and in a chain reaction, they set off hundreds of firecrackers in the racks, shelves and on the Slytherins' heads.

Madam Pince was screaming, the Slytherins were screaming, and the Gryffindors were roaring with laughter as they melted out of the door.

There, however, they found Argus Filch standing with a whip.

"None of you escapes," he hissed his furiously. "Follow me to the dungeons."

James and Sirius exchanged a look. They both knew that they could escape this moment with their friends if they wanted.

"But let's try it anyway—see the dungeons. Never saw them, did we?" whispered James.

"Nah. And there's Remus as backup."

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Remus had not come with them, as it was full moon that night.

When he came back the next afternoon, he saw an empty dormitory and almost empty common room.

"What happened to all of them?" he asked wonderingly to Lily.

"Locked in the dungeons by Filch," sniffed Lily.

"Sirius, James and Peter too?"

"Especially them. And Marlene and Alice too," said Lily, looking furious.

"Alice?"

"Yeah, as she's going out with Frank Longbottom."

"Really?"

"Why didn't you join them, anyway?" asked Lily suspiciously.

"Oh—just—just like that," said Remus. "Backup, y'know."

Remus sneaked down to the dungeons with his wand.

"Alohomora!" Having unlocked the door, he entered and saw half of Gryffindor tower chained there, looking slightly disgruntled.

"REMUS!" Everyone welcomed Remus enthusiastically. He unchained all of them.

"Now wait," he whispered. "I'll see if the way is clear."

Sirius clapped Remus on his shoulder. "Oh no, dear Moony. We have a plan," he said.

"What?" asked Remus in despair.

Five minutes later, Gryffindors were hiding in small groups behind pillars and armours on the way leading to the Slytherin common room near the dungeons.

As soon as any Slytherin came, the Gryffindors stupefied them, and the other groups dragged them into the dungeons and chained them in the same positions that they had been chained.

When about fifty Slytherins had been chained, Remus put a soundproof charm on the locked door. Then they sneaked away to their common room, snorting with laughter.

When Albus Dumbledore came back to the castle next morning, Argus Filch greeted him with serious complaints regarding the misbehavior of Gryffindor house.

Dumbledore went down to the dungeons with Filch and they found a bunch of highly indignant, furious and disgruntled Slytherins.

"I thought you said they were Gryffindors, Argus?" asked Dumbledore politely, with the hint of amusement in his voice.

Filch's eyes bulged. "They—they were Gryffindors—" he spluttered. "I don't know how—these—came here."

"Maybe we can ask them," said Dumbledore serenely. "Who locked you here?" He addressed the Slytherins.

"Don't—know," said Lucius Malfoy, fuming.

"It must have been Potter and Black!" shouted Snape suddenly, unable to restrain himself.

"Without proof, we cannot accept your word, Mr. Snape."

They were released, and no proof was ever obtained.

For the next week, Gryffindors kept giving superior looks to the Slytherins. And there was nothing the latter could do.