So, I got sudden inspiration while playing Pottermore...And watching Gossip Girl...And reading Doctor Who transcripts...
"Fred, why do you carry that with us? It's just a rubbish piece of old parchment."
"The why did Filch have it locked away, George? He wouldn't lock up an old parchment unless it did something."
"We've tried everything, Revealo, and any other revealing spell you could think of, nothing works."
"Well, something has to work, it has to be hiding something, all those witty comments aren't it, though."
"Yeah, it was nice reading what it had to say, though."
Come on, we're going to be late.
Fred and George, third years at Hogwarts School of Witchcraft and Wizardry, they ended up in Filch's, office after letting off some fire works in the Great Hall. Filch stepped out a moment and they looked through some things they probably shouldn't: The Items Filch had Taken Away From Younger Generations Jawer as they called it. They found an old piece of plank parchment that wouldn't show them what was on it, and insulted everybody who tried to read it. For the last few months they had tied everything they can to try to read it. When all else fails, don't give up. That's what they taught me.
"Mr. Weasleys, what are you doing this late?" McGonagall asked, walking up to them after hours.
Fred hurriedly put his wand in his pocket, noticing he rested it on the parchment.
"I solemnly swear, Micky, that I am up to no good. As for my not-as-good-looking brother, I'll let him speak for himself."
The conversation carried up until the boys got sent back to bed with detentions, Fred pulled out the parchment, why not try again?
"George, do you remember everything that was said in the last fifteen minutes?"
"Yes, why?"
Fred showed George the paper, "'Cuz something I said must've been right."
Discovering the parchment was a map that showed where everybody in the building was, they decided to finish their earlier expedition.
After putting the finishing touches on their prank for the Slytherins Fred pulled out the parchment, holding his wand underneath, "Well, George, Mischief Managed."
The parchment was, once again, blank and insulting. The boys went back to the Common Room, and spent the next fifteen minutes rehearsing the earlier conversation with their Head of House back wards, getting frustrated, Fred Said the first line after putting his wand back in his pocket, "I solemnly swear that I am up to no good."
Finishing my story, I put my parchment and quill down, capped off the ink and carried the candle to bed, "Klaus?"
A fairly young house elf appeared before me, "Yes, Mistress McGonagall?"
Well, I hope you liked my tale of the tale of Feorge's and Gred's discovery of The Marauder's Map.