The Golden Trio tore up the aisle between the desks of McGonagall's classroom and stopped in front of her desk, panting. After barely a moment Harry managed to get out urgently, "We need to see Professor Dumbledore, immediately!"
A bewildered McGonagall stared for a moment, then explained, "I'm afraid Professor Dumbledore is not here. He received an urgent owl from the Ministry of Magic and left immediately for London."
"He's gone?! Now?", Harry cried out in dismay, "But this is important! It's about the Philosopher's Stone!"
McGonagall's eyes widened in shock, and she managed to get out a feeble, "How do you know…?" before Harry cut her off.
"Somebody's going to try and steal it!" he blurted out, pleading with her to understand, but she was having none of it. Composing herself quickly, McGonagall gave him a stern glare.
"I don't know how you three found out about the stone, but I can assure you it is perfectly well-protected. Now would you go back to your dormitories? Quietly," she told them crisply before bending back over the essays she'd been grading.
Now, you must understand that Harry had been brushed off all his life. His teachers, his relatives, everyone he tried to tell something important to either thought he was lying or thought he was taking credit for what Dudley had done. He thought he had quashed down all the irritation and sadness at not being believed, but quashing something and hiding it away are remarkably similar.
And right now, being told that somebody stealing the most powerful alchemical artefact in the world was pure and utter hogwash brought those feelings back to the surface. So, with all the stress coming from worrying about the stone, and with that huge influx of emotion, something inside Harry just…snapped.
"No," he declared, straightening up, "We will not go back to our dormitories."
He placed his hands on her desk and reiterated, "Professor, we just told you that somebody is going to try to steal the Philosopher's Stone. An artefact that could be used in conjunction with ancient magicks to bring the Dark Lord Voldemort back to life."
McGonagall flinched at the name, but Harry continued undeterred. "An artefact that could be used to make unlimited amounts of gold, and therefore destroy the carefully-balanced economy of the entire Wizarding World. We tell you that it's going to be stolen, and you just brush us off like dust off your robes. Well I won't stand for it!"
He grabbed the wrists of both McGonagall and Ron, who had Hermione clutching onto his forearm, and with a huge influx of power and a crack that echoed throughout the entire castle, he broke through the ancient wards and Apparated to the third-floor corridor on the right-hand side.
"This is the door that leads to the room Fluffy is in," Harry told McGonagall when everyone had regained their bearings, "Hermione opened it with a first-year Alohomora."
He himself then opened it with an Alohomora, and McGonagall's eye widened. They widened further when she saw Fluffy, but Harry simply took out a pre-charmed guitar he had bought in Diagon Alley and tapped it with his wand.
A soothing melody began resonating from the strings, and soon Fluffy was snoring peacefully. Harry levitated the dog's paw out of the way and opened the trapdoor, taking out another store-bought bauble. It was a witch-light, 'rather fitting' he had thought at the time, and when he tapped it with his wand it lit up. He dropped it down the hole and, after a few seconds, it hit the bottom of the shaft.
"A soft and squishy plant to soften the fall and put a thief into a false sense of security. The plant itself is probably very deadly, though. Hermione?" Harry asked his friend, and she replied promptly.
"Devil's Snare, a deceptively deadly plant that binds and strangles its victims before they can react. It dislikes heat and light," she told him, and Harry gave a short hum before shooting an Incendio down at it. The plant withered and shied away from the flames, and Harry jumped down without further ado. Near the bottom he cast Wingardium Leviosa on his clothes and settled softly on the floor, then levitated the other three down.
"Mr. Potter, I must ask what the meaning of this is!" McGonagall demanded, and Harry looked over his shoulder with an almost bored expression.
"A first year just made it past two of your so-called 'impenetrable defenses' in five minutes flat, just to prove you wrong. Imagine if it was someone who wanted to actually get the Stone," he said to her, giving McGonagall something to think about. She didn't speak again until they emerged from the hall and found themselves in a large, circular chamber.
"Flitwick's defense," McGonagall said automatically, "Flying keys charmed to attack anybody who mounts those brooms over there."
She pointed at said brooms, but Harry wasn't interested.
"Immobulus," he said almost lazily, then, "Accio key for that door."
A huge, rusty key with a bent wing zoomed into his hand, weaving around the immobilized others. He inserted it into the lock and opened the door, gesturing graciously for the other three to enter. They did so with no small amount of hesitation.
A short hallway later they found themselves in a dimly lit room, torches flaring a moment later to reveal a chessboard. "Well this is just suspicious," Harry commented offhandedly, and McGonagall looked at him sharply.
"I'm sorry, Mister Potter?" she asked him frostily, and he gave her a serene smile.
"I bet Dumbledore suggested this, right? Well, it just so happens that one of my best friends is the best chess player Hogwarts has ever seen," he said, ignoring Ron's puffing up in pride, "He'd have no problem playing across if it came to that. As it is…"
He trailed off and simply walked around the board by way of the trench defeated pieces were sent to, stepping carefully over the shards of the pieces there. The others followed, McGonagall blushing sheepishly.
The door behind the line of black pieces opened into a horrible-smelling room, and in the middle of that room sat a fully-grown mountain troll. "I think we've already established we could take care of this with Wingardium Leviosa," Harry said, and with a twist of his wand and a whisper of, "Somnium," the troll was sent to sleep. He walked briskly to the other door, the others following with their robes over their noses and their eyes darting between the troll and Harry.
The third room Harry ignored the potions completely, saying as the flames sprang up, "My History of Magic textbook mentioned that witches and wizards escaped the Salem witch burnings with flame-freezing charms, so I looked one up," he explained, and with a muttered, "Frigidus Ignis,", he simply walked through the black flames. The others followed after McGonagall cast the same spell on them, and down a short flight of steps was a large oblong room with the Mirror of Erised in the middle.
"Here we are, the room containing the Stone!" Harry exclaimed happily, walking forward to gaze into the Mirror. He stood there for a few moments, then told them, "This is the Mirror of Erised, an enchanted mirror that shows what you want most."
He pointed at the inscription on the top of the Mirror, reciting, "I show not your face, but your heart's desire. This is probably the only thing that would stump anyone trying to get the Stone. Stump, but not defeat."
Looking the Mirror up and down, Harry continued, "Professor Dumbledore probably wanted to capture the person trying to steal the Stone, not stop them."
"Well done, Mr. Potter," a voice drawled from behind them, and three of the four whirled around in alarm. Harry simply turned with an air of in-control calmness and came face to face with…a sarcastically-clapping Professor Quirrel.
"Hey Squirrel," Harry said nonchalantly, giving a small smile as the possessed teacher twitched, "Come for the Stone, have you?"
Quirrel raised an eyebrow and said, "Very good, Mr. Potter. How did you guess it was me?"
"Hmm, let's see," Harry began with the tone of somebody stating the obvious, "Whenever you're near my scar starts to hurt, said scar was given to me by the most evil Dark Lord in a century, and that turban you got from the African tribe? No African tribe I know of uses turbans as a reward. Not to mention that cliché garlic-with-a-hint-of-undead smell."
He shrugged and added, "Besides, nobody that seemingly pathetic couldn't not be evil. So, who's that on the back of your head, then?"
Professor McGonagall looked at Harry in alarm, but Quirrel merely smiled and reached up, beginning to unwind his turban. Hermione, who had switched from Ron to Harry when she saw how in-control he was, clutched his arm in fright as the Professor slash professional actor drew the big reveal out further than was strictly necessary.
Harry finally got tired of waiting and shot an Incendio at the turban.
"GYAH!" Quirrel yelled, unwinding the flaming turban faster. He had no doubt used an Undetectable Expansion charm because the thing went on further than should have been possible for a turban of that size, but finally he got to the end and flung in on the ground. Panting slightly, Quirrel ground out a, "Have you no patience, Mr. Potter?"
"I'm eleven," Harry answered cheerfully.
Quirrel gave him a flat look as he deadpanned, "Right."
Clearing his throat and composing his face, he continued, "So, Mr. Potter, you know why I am here. Give me the Stone and you won't what am I standing in?" he suddenly broke off. He had been slowly stalking forward, and his foot had landed in a rather large puddle of red liquid.
"Would you believe it's strawberry milkshake?" Harry asked him innocently, and Quirrel shot him a glare.
"No," he deadpanned, and Harry pouted
"Gryffindor courage?" the raven proposed, and Quirrel glared harder.
"No," he reiterated, raising his voice.
"Dungeon nectar?" Harry put forth, and Quirrel gave a wordless snarl.
"Mr. Potter!" he demanded loudly.
Harry sighed and relented, "Fine. It's that lovely Slytherin couple from seventh year."
You could hear the surprised blinks.
"Come again?" Quirrel said after a moment, but Harry only shrugged.
"They were threatening me," he said, as if that explained everything, and Quirrel looked down at the mess coating his shoes half in wonder and half in fear.
"How did you even do this? You're a first year!" he exclaimed.
"A dollop of fairy dust," Harry confided with a smile, and Quirrel gave him a look.
"Seriously, Mr. Potter," he said patiently, and Harry smiled wider.
"I ripped the tag off a mattress," he replied immediately.
"Mr. Potter," Quirrel said more firmly, and Harry stuck his tongue between his teeth.
"A clothespin and some ingenuity," he told the professor.
"Mr. Potter!" Quirrel yelled, and Harry tilted his head.
"Yes?" he asked pleasantly.
"I demand you tell me how you-", Quirrel began, but he was cut off by Harry's yell of, "Now!"
Hermione had been sneaking off to the side inconspicuously, and at Harry's yell she pulled a lever hiding behind a pillar. The floor underneath Quirrel vanished, and he fell into a dark hole.
"Well, that went well," Harry said with satisfaction, Ron and Hermione nodding happily, "Come on guys, it's dinner time!"
Dramatic music came out of nowhere, and lightning flashed across the ceiling.
"…Well alright then," Harry said after a moment.
"Now hold on!", McGonagall protested after a moment of gathering her thoughts, "What…what just happened?!"
"We trapped Quirrel in a hole," Harry said with that 'duh' tone.
"Well, yes, but…how?!" she asked helplessly, and Harry beamed.
"Trial and error, Professor," he told her, but then his smile dimmed a little as he amended, "…Mostly error."
-Earlier-
"Pull the lever, Ron!" Harry commanded, and Ron pulled the lever. "Wrong leveeeeeerrrr…!" Harry's yell echoed from the hole.
-Now-
"Why did you even have that letter?" Hermione asked curiously, and Harry admitted cheerfully, "I've no idea."
"Right!" McGonagall interrupted loudly, "So, what's this?", gesturing to the mess Quirrel had stepped in.
"Strawberry jam," Harry said with a laugh, and Professor McGonagall sighed in relief.
"Oh, good," she said, and Scourgify'd it away.
-Later-
Professor McGonagall was just tucking into her supper when Professor Dumbledore tapped his glass. "I have just been informed that two of our Seventh Year Slytherins have gone missing. If anyone has any information, please inform a teacher."
McGonagall blinked a couple of times, looked to the cheerfully-waving Golden Trio, and pushed her plate away from her.