George drew his wand, tapped the parchment gently, and said:
"I solemnly swear that I am up to no good!"
In an instant, Harry saw fine lines of ink spread like a spiderweb from the spot George's wand had touched, connecting and crisscrossing until they reached every corner of the parchment.
Then large, green, ornate letters appeared at the top of the parchment.
But before he could read them, George, whether deliberately or not, gripped the lettered section and covered the topmost line. Harry could only see the words, "Messrs., purveyors of aids to magical mischief-makers, are proud to present-the Marauder's Map."
Harry saw that the map depicted every detail of Hogwarts Castle and its grounds. Many little black dots moved across it, with tiny lettering beside them, but before Harry could make it out-
George pointed his wand at the Marauder's Map again and said, "Mischief Managed!"
The ink lines and little black dots quickly vanished.
Harry froze for a moment, then looked at George.
Beside him, Fred said with a smile:
"The Marauder's Map doesn't just mark Hogwarts' layout and some secret passages nobody knows about. It also shows everyone's location in real time, including Headmaster Dumbledore."
George continued:
"We've been using it all term to monitor every passage leading out of the school, to stop Black from sneaking into Hogwarts through them."
Harry swallowed and said cautiously:
"So..."
George and Fred exchanged smiles, then Fred picked up the wooden box on the nearby table and winked.
"The Marauder's Map was designed and made by a very remarkable gentleman during his school days, specifically to point lost young people like us in the right direction..."
"But getting it requires a little ritual, one that gentleman created himself."
Thinking of where the map had come from, Harry said in