The Curse of Luna (The Marauders)

Alaska Lenis never once imagined herself apologizing to one of her best friends' horrid brother - Sirius Black, and his obnoxious group of friends.

But boring late-summer afternoons that strengthened her playful curiosity led to her crossing the line of inquisitiveness and reaching simple nosiness, which made her accidentally (or maybe not So accidentally) discover one of the self-proclaimed Marauders' best kept secrets.

Tangled into this mess of an apologetic relationship with the Hogwarts pranksters who, she now knows, hide a lot more under the surface, gained her, yet another, secret of her own as she tries to gain forgiveness of Sirius Black, only hoping that she won't have to do the same with the other Black brother.

She still refuses to return the map however. Tho she does offer a lot of money in return, which they seemed ridiculously insulted by.

or, if you'd prefer:

Alaska Lenis, model student & secretly a seer, stumbles upon a, at first glance, regular piece of parchment which turns out to be one of the most prized possessions of its founders. All the insults & hints it starts giving in return to her attempts to figure it out, keep her up at night as she tries to unravel the mystery that hides behind it.