Barely had Oleandra walked a few paces from the Charms classroom when she pulled out the Marauder's Map and tapped the parchment with her wand. The corridor was deserted, and she knew exactly where Loki would be for the next hour and a half, which made this the perfect moment to experiment.
"I solemnly swear that I am up to no good," she whispered.
Thankfully, plotting against a fellow student did count towards the 'up to no good' requirement of the Marauder's Map's activation phrase. Since Oleandra was unable to vocalise lies, the map was about as useful as tissue paper when she was not actually planning anything nefarious, as she had discovered the previous night, when she tried to open it simply to see how her little sister Astoria was doing.
The yellowed parchment suddenly took on a silvery sheen, and, like a children's pop-up book for Muggles, the map's usual greeting sprang from the paper in three-dimensional letters:
"Messrs Moony, Wormtail, Padfoot, and Prongs, Purveyors of Aids to Magical Mischief-Makers, are proud to present, with the welcome assistance of Mme Bright-Eyes… The New Marauder's Map."
Oleandra's cheeks flushed pink with embarrassment. For some reason, the Marauder's Map had seen fit to acknowledge her role in its upgrade by crediting her as a helper and assigning her a nickname… one which, for the record, she had not chosen herself. She could not help but cringe slightly every time those silver lines appeared.
"I wonder what Harry would say if he saw what I've done to his father's precious map," she muttered to herself. "I'm not sure he'd approve…"
For one thing, the map in its opened state was far less stealthy than the original, thanks to its newly acquired silvery sheen; it was rather striking when caught in direct sunlight. Indeed, the Marauder's Map now showed the castle much as the Map Chamber's map pool did, while retaining its original function of tracking the movements of everyone within the grounds.
But that wasn't all it could do.
By making their map from a scrap of stolen parchment taken from the Book of Admittance, and inking it with ink from the Quill of Acceptance, the Marauders ensured that the enchantments laid upon it would bypass Hogwarts's Untraceability and Unplottability wards, allowing them to pry wide open the castle's veil of privacy… yet, judging by the fact that the map itself had requested Oleandra drop it into the Map Chamber's silver pool, its already impressive powers were not where the Marauders' ambitions for it ended.
Evidently, assuming direct control over the castle had been the Marauders' ultimate goal, one they had fortunately never managed to accomplish before their graduation, due to the Map Chamber's inaccessibility.
By allowing it to link itself to Hogwarts's nexus of power, Oleandra had effectively granted the Marauder's Map administrative rights over the castle's enchantments… and the possibilities were endless.
…
The Grand Staircase was Oleandra's first destination to confirm if the Marauder's Map could truly influence the castle's facilities. Since most students were supposed to be in class at this time, save for those who had free periods, this was the perfect time to test out the map's new powers.
"Grand Staircase, please," Oleandra said clearly.
A translucent projection of the tower sprang from the map's shiny, metallic surface. Looking more closely, Oleandra spotted a few students whose names she did not recognise wandering the seventh floor— doubtlessly first-years who had become trapped there on their way to class.
Taking pity on them, Oleandra reached into the translucent tower display and gently pinched the miniature stairs between her fingers, dragging them into alignment to allow the students to descend to the sixth floor, where they would have more options to continue downwards. She then looked up and saw the topmost set of stairs rumbling into motion, following the path she had set for them.
Oleandra then directed her gaze to the stairs linking the Great Hall to the Grand Staircase's central pillar. If those stairs refused to swing into alignment, she would, in effect, be able to isolate the Great Hall from the rest of the school… save for anyone with the ability to fly.
"The Hallowe'en feast," Oleandra murmured to herself. "Everyone will be there."
Under normal circumstances, students and staff would be scattered throughout the school, even at meal times. Some students might forego eating to study in the library, or teachers might remain in their offices to catch up on grading… yet very few would willingly miss a feast.
"Now, I just need to find some way to lure out Loki, before or during the feast," Oleandra thought out loud. "Then, no one will be able to come to his rescue."
Disable the magic flowing to the paintings, so they could not tell on her.
Disable the stairs, preventing anyone from joining the fight.
Gather the castle's gargoyles and have them fight on her behalf.
And finally, spring the trap, disabling the runic magic of the stars by flooding the Grand Staircase with telluric energy straight from the Earth's core… which she admittedly hadn't figured out how to do yet.
"Only a few days left until October 31st," Oleandra muttered to herself. "I'll need to get busy…"
And so, over the next few days, the castle's gargoyles began to vanish from their usual perches, leaving a few curious students to wonder where they had wandered off to… but the majority of the student body either did not notice or did not care enough to give this unusual phenomenon a second thought.
…
The Grand Staircase would be the location of their duel.
The thought of murdering Loki in his bed while he slept had briefly crossed her mind, but she had dismissed the idea as too risky. She might very well succeed by disabling his runic magic, but she had no idea which wards he might have added since she had sneaked into his room to steal back Harry's Invisibility Cloak.
In any case, she did not think she could manage to kill him there without escaping detection. Executing a perfect murder while wading through Loki's other, unknown protective enchantments, without waking Crabbe and Goyle, and without being identified as the culprit... Her designs for Hogwarts were not yet complete, and she could not afford to be chased out just yet.