A stone that gives life is an odd concept at the best of times. Why a stone? Why not a chalice, or a ring, or maybe even a specific design for a tattoo? Something you can't easily misplace would be a much better idea than a stone. Unless, of course, the stone could find itself, but that's as preposterous as hatching a snake from a chicken's egg.
Oh, wait…
In any case, Harry Potter had just left his friends, Ron Weasley and Hermione Granger, behind a wall of flames that barred their entrance. Harry had told them it was because Ron needed help with his injuries, but he had really only fallen a few feet at most, and he could still walk with them to Snape's logic puzzle perfectly fine. The White Queen hadn't even touched him, for Merlin's sake! But Harry insisted that he must have hit his head on the way down, had a concussion, and was therefore unable to face Lord Voldemort.
"And Hermione, really? Leaving poor, injured Ron all alone and defenseless while you take a right merry jaunt with me through a raging inferno of flames? That's just a tad selfish." Harry sniffed disdainfully, sticking his nose up and turning his head away, but Hermione merely smiled sadly and went up to him.
"It takes more than spells to be a great wizard, Harry." she told him softly, laying a light kiss on his cheek before fleeing back the way they had come to send a message to Dumbledore.
"Blimey, mate." Ron said in awe, looking at the fire Hermione had disappeared into, before smirking and leaning on the shorter boy's shoulder, "You make all the girls run away like that?"
"Sit down, you're injured!" Harry yelled angrily, smacking Ron upside the head and tripping him to the ground. Then he huffed irritably and stalked through the potions room to the door leading forward.
He walked in silence, the only sounds being the crackling of torches and his shoes thudding onto the ground, until his hallway suddenly opened up onto a flight of shallow steps. Cautiously stepping down, one at a time, he was surprised to see that it was Quirrel, not Snape, standing in front of the Mirror of Erised.
The mumbling was a bit disconcerting, but Harry pressed on.
He managed to step close enough to the Professor to make out his mutterings of complex magical formulae and, oddly enough, the mating habits of penguins, before Professor Quirrel noticed the scuffing of his shoes and whirled around. His eyes, panicked and feral, slowly calmed to a look of contempt amusement, and he smirked ever-so-slightly.
"I was wondering whether I'd be seeing you here, Potter." he said conversationally, crossing his arms with a casual air.
"Can't say I've wondered the same, Professor." he replied neutrally, flicking his gaze around at the circular, mostly-empty room before quickly looking back to Quirrel, "I would have thought Snape would be in your place."
"Yes, wouldn't you?" Quirrel drawled derisively, then mocked, "Because really, who would ever suspect p-poor, st-st-stuttering Professor Quirrel?"
"Obviously not me." Harry replied sardonically, mentally slapping himself for his oversight. Really, somebody that pathetic couldn't not be evil.
"Indeed." Quirrel said dryly before seemingly losing interest and turning back to the Mirror. "Now, what does this Mirror do?" Quirrel asked, partly to Harry and partly to himself, and Harry saw no harm in telling him.
"It's called the Mirror of Erised." he supplied helpfully, "It shows not your reflection, but your heart's desire."
"Poetic, but how do I get the Stone out, then?" Quirrel snapped, but Harry merely shrugged and walked up to stand beside Quirrel.
"I dunno. You're the teacher." Harry said lightly, gazing into the Mirror's depths. The mist that usually fogged the Mirror was beginning to clear, and he was interested in what it showed.
Quirrel didn't notice when Harry's eyes widened ever-so-slightly. He didn't notice when he tilted his head to the side curiously, as if listening to something. He didn't notice when Harry grinned widely and stuck his hands in his pockets.
He did notice, though, when he took the Philosopher's Stone out and threw it up into the air.
"Protocol sixty-three! Execute!" he shouted, and the fire burning ominously in their wall sconces was snuffed out as the magic sustaining them was drawn into the Stone. Enchanted wind swirled around in a howling vortex of arcane force, the Stone glowing fiercely at the eye of this mystic storm, until suddenly the wind stopped and the light vanished.
After stumbling around in the darkness for a full five minutes, Quirrel finally remembered that he was a wizard and lit his wand. What he saw was...odd.
Harry Potter was sitting at a conjured table, sipping some tea and happily chatting with a girl that most definitely had not been there before. Her long hair was a blood-red, her eyes the same, and she was wearing a sturdy-looking leather tunic over slightly thinner leather pants. Comfortable-looking shoes adorned her feet, and a right enormous sword was strapped to her back. The entire outfit was obviously enchanted, flowing like water around her body, and the sword emitted a faint glow from its sheath.
"And then she sort of twirled it, like so..." the girl was explaining to Harry, "and then I could hear its voice in my head! It was so weird!"
Harry giggled a bit and informed her, "You think that's bad, you should try sitting in front of the entire school with it on your head. Every second up there, you're afraid it'll burst out laughing and go, 'Pfah, you're a bedwetter!'."
"Oh wow. That is horrible." she laughed, then slapped a hand over her mouth as a thought occurred to her. At Harry's inquiring glance, she explained with a grin, "Imagine what it'd be like if you were Sorted when you were older." casually making an obscene hand gesture.
"Oh, Merlin! Thank Gods for childhood innocence, then. That poor Hat!" Harry exclaimed, beginning to giggle again when her hands didn't stop. She grinned and, quick as a flash, bopped him on the nose with a finger. Harry laughed harder.
"What do you think you're doing, Potter?! Where is the Stone?!" Quirrel yelled furiously.
The girl slowly turned her head to look with disdain upon the man that would so harshly address her friend, her blood-red gaze piercing through him much as his master's had, and with contempt veritably dripping from her voice she questioned, "Harry dear, who is this leaf of a man exuding dark Soul magic in waves?"
"Hm? Oh, that's Professor Quirrel. He was trying to steal the Philosopher's Stone." Harry said conversationally, then lit up in a bright grin and exclaimed, "But then the nice spirit inside the Mirror told me how to summon you, and you have a bloody great sword, and it's just so bloody cool, so I don't think you have to worry about that anymore!"
The girl, blushing from his glowing review of her, cleared her throat and faltered, "Yes, er, well, be that as it may, I'd feel much better if he wasn't around to threaten you."
And with that, she executed a beautifully fluid motion that allowed her to, in less than a second, draw her sword from her sheath, point it at Quirrel, and intone, "Purify."
The wall of pure healing magic that slammed into the possessed Professor purged him of thirteen behavior-altering spells, three tracking charms, a mind-control spell similar to the Imperius, a self-renewing snowball charm from the Weasley twins, and one errant wraith, which howled around the room in a fury for a few moments before flying through the wall.
Quirrel collapsed to the floor in a dead faint.
"Well that happened." Harry said flatly.
The girl laughed and said, "Yes it did." standing up and Vanishing the table, "And now I think it's time for you to return to your friends."
"Awww! But I wanna stay and talk to you more!" Harry pouted, slumping in his seat and crossing his arms. The girl smirked and Vanished that, too, sending Harry sprawling to the ground. He sat up and glared at her, making her laugh.
"I know you do, but think of it like looking in the Mirror." she said, going up to the Mirror. "It's nice while it lasts, but eventually-" she stopped to take out her sword, plunging it into the Mirror farther than Harry thought possible, "-you have to look away."
The fog in the mirror began to drain towards the sword, the glass dimming until it appeared to just be a regular mirror. Her sword's glow took on an orange tint, and as she slowly withdrew it, the Mirror crumbled to dust.
"Ooooooh!" Harry cat-called, "You're gonna be in troooouuubllllle!"
The girl snickered and shook her head, walking back over to Harry and crossing her arms.
"So," she started, ",who exactly do you think I am?"
"Well, the spirit inside the Mirror of Erised told me that you're one of Death's disciples, the personification of immortality. By the way, I hope you got the spirit out of the Mirror before you broke it." Harry said reprovingly to the amused warrior.
"I did, and it's very happy with its new home. That is correct, but did it tell you my name?" she pressed importantly, widening her eyes in an effort to convey the importance of this matter.
"Uhm, not your actual name, no." Harry admitted, and the girl nodded decisively.
"Alright then. My name is Fidelius-protected, and the fact that the Mirror couldn't tell you is proof it still works." she explained, "A Fidelius Charm hides a piece of information within a person's soul. Only the Secret Keeper can tell someone else, and I'm the only Secret Keeper for my name. If you ever need me, call me either out loud or in your head, and I'll hear you."
Harry nodded quickly at the influx of information, and the girl flashed a quick smile at him before assuming a solemn air.
"My name...is Verity." she said seriously, and Harry felt a peculiar sort of magic settle around the word in his head. A moment later, Verity drew her sword and quickly slashed it down, tearing the very space in front of them in half. She pushed him through the ragged edges, a bright, "Bye Harry!" following him, before making an odd hand sigil that closed the gap easily.
Harry was immediately beset by a frantic bushy-haired girl, an even more frantic nurse, and a merrily-twinkling Headmaster, all in varying degrees of panic and all very-much wanting an explanation.
Verity stood in the dungeons for a long time, staring at the space the gap had occupied and thinking over the conversation she had had with the Fates and Death before they had sent her back to life.
"Oh Harry..." she muttered, "...you poor thing. Forced to...to..." but she broke off with an angry growl before she could finish the thought. Calming herself quickly, for such behavior did not befit a warrior like her, thank you very much, she made a vow, right then and there.
"I, Verity Tallor Marick, do swear upon my unlife and magic that I will help the one I know as Harry James Potter whenever and however I can. I further vow that immortality will not seek him until he is ready. So I have said it, so mote it be."
And so, with the ancient magicks fluttering around her in praise and the enraged howls of the Fates and Death ringing in her ears, Verity made a particularly rude hand gesture to a patch of empty air and vanished soundlessly.
Quirrel was found the next morning, totally fine but for some peculiar instances of lost time.