Homonculous

Messrs Moony, Wormtail, Padfoot, and Prongs certainly feel quite accomplished after completing what they dub as the Marauder's Map. A map designed to show every classroom, hall, corridor, and even secret passageway of the Hogwarts Castle but also capable of identifying every person, ghost, and poltergeist roaming about.

Or so they thought.

It takes Elspeth Hayes casually strolling down the corridor one afternoon for the boys to realise that she's not showing up on the map and they want to figure out why. But Elspeth is not about to give away her secrets so easily, after all, a girl has to have her secrets to keep the boys on their toes.