It had been half an hour
and no one had shown up.
Julian sat slumped in a chair in the room of requirement, music playing from an old record player. The room had all the trappings of a party but absolutely none of the people. He had tried the "keep it small" trick, telling only a few people about the party and hoping it would spread. Apparently, he had divulged the secret to Hogwart's best secret keepers.
He sighed, deciding to give up and stood, crossing for the door. As he reached out, the door swung open, revealing the infamous pair of Margo Richards and Molly Weasley. "Julie!" Margo squealed, throwing her arms around him and pulling him into a hug - let's be real, he needed that. He managed a muffled greeting to the girls when Margo gasped, pushing him away and saying, "Where is everybody?! Did they cancel?"
"No, I-"
"Did you change the time?"
"Thing is-"
"Is there another room-"
"Margo." It was Molly's quiet voice that finally made Margo realize what the deal was. She took in the party and then squared her shoulders.
"No matter. Molly, you-"
"Got it. Out."
Margo grinned and turned, grabbing Julian's hand and dragging him out. "Look. Go. Change into a black button up, black trousers... You got a bow tie?"
"Aren't bow ties lame?"
"Not on you, it'd be endearing. Red bow tie, red sneakers. You'll be a picture. I'll go stir up trouble with my people, you announce that Molly's got some stuff in the Room of Requirement, and make sure you emphasize stuff. People will follow." He opened his mouth and she answered, "Molly's giving the room a makeover. It'll look awesome. Okay, go!"
Half an hour later, Julian had dressed as Margo commanded and made his announcement. To his surprise, the common room burst into a mess of excitement. Peter asked Julian to wait up, but Julian trusted his instinct and called out, "Can't! Ladies are waiting."
When he slipped into the Room of Requirement, he was shocked at the transformation. It had a home-y look, with couches and beanbags littering the room, and a table full of snacks and bottles of alcohol. Molly was smoking in the corner, talking to someone in her house, and Margo abandoned a pair of Hufflepuffs to drag Julian in. "You look precious! I mean, manly. Very manly. Look, Molly and I were able to collect some drinks, get some food, and she totally made over the vibe. There's a closet for whatever," she said, giving a devious look, "and we'll start drinking games if people get bored.
Julian mouthed in shock before finally croaking, "Blimey, Margo! This is... I mean, it's... It's an actual party."
Margo smiled a sugary smile. "It's what I do."
((Sorry for the wall of text. Your character can either show up or already be there. It's just getting into full swing and you bet the girls anticipated your character's every hedonistic need. Go wild!))