Item from harry-potter-goblet-of-fire by
A magical map of Hogwarts showing every person, passage, and room in real time — this year it reveals Barty Crouch's name in Snape's office, a clue Harry sees but cannot interpret until it's too late.
The Map shows Harry something he cannot explain: the name 'Bartemius Crouch' moving through the castle at night, specifically in Snape's office. Harry assumes it's Barty Crouch Sr — the Ministry official — sneaking around, which is strange but not impossible. He mentions it to people who don't follow up. He doesn't realize the Map is showing him Barty Crouch Jr, because the Map shows true identities and cannot be fooled by Polyjuice Potion. This is the Map's cruelest trick this year — it shows Harry the truth and he looks right at it and doesn't understand. The name 'Bartemius Crouch' on a dot in Snape's office should have been the key to everything. The Map created by the Marauders cannot lie, but it can only show what's there. It cannot force the reader to comprehend.
When blank, a worn piece of old parchment. Tap it with a wand and say 'I solemnly swear that I am up to no good' and thin ink lines spread, forming a complete real-time map of Hogwarts. Every person appears as a tiny labeled dot. 'Mischief managed' wipes it clean.
Also known as: the Marauder's Map, Marauder's Map, the Map