Oleandra froze in place, remembering the Dusk Elves' fates at her hands. She quickly shook away the visions of blood and gore that flew before her eyes. She and the Lethifold were bonded; if she were to be directly struck by a Spirit Guardian multiple times in this state, then she would suffer the same fate as the Elves she had inadvertently killed; eaten alive.
"I suppose it wouldn't hurt to hear you out," said Oleandra uneasily, which earned her strange stares from the three Gryffindors. She'd been raring to go, why was she giving up now?
"We can't trust them," insisted Hermione. "I knew I wasn't the only one to have guessed it… Harry, he wants you dead too— he's a werewolf! He must have been helping Black get into the castle!"
"Not at all up to your usual standard, Hermione," he tut-tutted her. "Only one out of three, I'm afraid. I have not been helping Sirius get into the castle and I certainly don't want Harry dead…"
For a moment there, Lupin seemed to experience a slight spasm.
"But I won't deny that I am a werewolf," he finished.
"Right!" said Oleandra automatically. "Tonight's a full moon. He's even more dangerous tonight!"
"No, no, no!" said Lupin, his facing emptying itself of colour. "I left without taking my Wolfsbane potion; Snape was supposed to bring it to me!"
"Snape's here?" snarled Black. "All the more reason to hurry up. Let's kill him and be done with it!"
"We won't let you kill Harry," moaned Ron, as he tried to get up once more. "We've told you."
"Oleandra," said Lupin thoughtfully. "I've seen you fly, even under Hogwarts's restrictions. Snape's sure to have brought the potion to my office by now; could you go and fetch it for me?"
"Not a chance," replied Oleandra. "And leave these three to fend for themselves? Besides, you'll be easier to take down as a mindless beast."
"You don't want to meet my other self," sighed Lupin, tossing back the Gryffindors' wands back to them. "But fine, you win. Sirius, give Oleandra her wand back."
Black seemed reluctant at the idea of handing a Slytherin their weapon back, but he did so anyway.
"Happy now? You're all armed, while we're not," said Lupin. "Now, I need to make this quick. A while back, I confiscated Harry's Marauder's Map. Tonight, I was in my office, examining it, since I was sure that these three," Lupin waved towards the Gryffindor Trio, "would sneak out to see Hagrid before his Hippogriff was executed."
"You know how to work it?" said Harry suspiciously.
"Of course I do," said Lupin urgently. "I helped write it; along with my three other best friends; Peter Pettigrew, Sirius here, and… your father, Harry. I was worried about you sneaking out under your Invisibility Cloak—"
"How'd you know—"
"Haven't you been listening?" said Lupin impatiently. "I just told you we were all friends with your father— you inherited James's cloak. Obviously, I know about it."
Oleandra was getting a little confused; she already knew about the Invisibility Cloak; she had learned about it when Harry accidentally revealed his head the last time they visited the Shrieking Shack. She even had it in her possession right now. But the Marauder's Map? She'd never heard of it. How many magical items did Harry have, anyway?
"So, what is this Marauder's Map?" Oleandra asked.
"It's a magical map the four of us wrote back when we attended Hogwarts," Lupin explained. "It shows the location and name of every single person in Hogwarts in real time, on top of mapping out the entirety of Hogwarts."
"How in the world did you make such a thing as students?" said Oleandra suspiciously. "That seems like incredibly complex magic. Not to mention that the existence of such an item is an incredibly offensive invasion of privacy."
"This isn't the time to be discussing magical item manufacturing!" growled Black.
"Please, Sirius, we need to earn their confidence," said Lupin soothingly. "Oleandra, to answer your question… we cheated. Apart from me, we're all Animagi; it's incredibly easy for us to sneak into places where we don't belong. Peter stole for us— er, borrowed the Quill of Acceptance and we ripped out a page from the Book of Acceptance in Professor McGonagall's office; from there, it was only too easy to create a map that knows everything that goes on in Hogwarts."
"That's genius," said Hermione, half-outraged at the desecration of a sacred Hogwarts artefact and half-amazed at the genius required to lead such a plan to success. "The magic of names; those two items record all of the magical children in the British Isles, so that the school can send them acceptance letters! No wonder it works as it does!"
"Now that we're all caught up to speed," Lupin said, "as I was saying, I was inspecting the Marauder's Map. And you can imagine my surprise when I saw you join up with a dot on the map labelled… Peter Pettigrew."
"That's impossible!" said Harry. "Nobody joined up with us, except Oleandra." Harry pointed at Sirius Black. "And he's the one who killed him!"
"Remember what I said about my friends all being Animagi?" said Lupin, looking straight at Ron. "Care to take a guess at which animal Peter turns into?"
"No. No, no, no!" cried Ron. "Scabbers has nothing to do with your crazy stories. You're all bloody barmy! You've gone moon-addled! You're a bunch of dangerous lunatics!"
"Is it really so crazy?" said Lupin. "What's the harm in letting us get a proper look at your rat?"
"C'mon, let's just kill him," growled Black.
"Sirius, please, you're not helping our case," said Lupin soothingly.
"Listen," Ron insisted. "Scabbers has been with my family for twelve years. He's always been our pet rat."
"He's not a rat," croaked Sirius Black. "He's a Wizard named Peter Pettigrew!"
"You're definitely mental," said Ron, shivering.
"This is ridiculous," added Hermione.
"You murdered Pettigrew," said Harry. "You killed him twelve years…"
Harry's voice trailed off. Twelve? How many years had Ron said he'd had Scabbers, again?
"I meant to kill him," growled Black, "but he got the better of me… and now, I intend to commit the murder I was imprisoned for!"
Black lunged at Ron, making Crookshanks fall off of him.
"Sirius, NO!" Lupin yelled.
You know my style, by now; I love coming up with theories for the gaping holes of unexplained lore. How did the four Marauders create such a powerful map, that can even track Dumbledore in his office?
It always struck me as strange; both of Harry's parents were geniuses in their own rights, but Harry's so painfully average. Well, at least until he gets some training under his belt in book 4.
So my answer is that the Marauders weren't quite as amazing as the rumours said they were; James, Lupin, Sirius and Peter, cheated; they used two powerful artefacts with the magic to track all names to create their Marauder's Map: the Book and Quill of Acceptance.
Still very impressive, but still doable for students.