The polyjuice problem
tf by magic - weight gain
The Slytherin common room disappeared behind them as Harry and Ron hurried through the deserted corridors, each struggling to keep pace with the last fading moments of the Polyjuice Potion.
Harry could already feel it. A strange warmth spread beneath his skin. His shoulders tightened, then narrowed. His hands shrank around the oversized sleeves of Goyle's robes.
"We've got to get back!" Ron whispered, his voice already rising toward his own. "It's wearing off!"
They slipped into Moaning Myrtle's bathroom just as Harry's knees buckled.
Both transformations happened almost simultaneously. Bones cracked softly. Heavy muscles melted away. Their uniforms hanged awkwardly from their suddenly smaller bodies. Harry stumbled against one of the sinks.
His vision blurred—
Then sharpened.
He blinked instinctively before realizing he needed his glasses again. Ron rubbed his own face in relief.
"Oh, thank Merlin..." he muttered. "I thought Malfoy was going to notice something."
Harry barely answered. Instead, he stared at his own hands. Thin. Scarred. Familiar. He flexed his fingers once. Something about them suddenly felt... surprisingly fragile.
"You alright?" Ron asked.
Harry looked up a second later.
"Yeah."
The answer came a little too quickly.
"I just..."
He hesitated.
"...forgot what it was like."
Ron laughed.
"I didn't. I hated every second of being Crabbe."
Harry forced a smile.
"I suppose."
At that moment the bathroom door burst open. Hermione stumbled inside. Or rather— Half-Hermione. Her face was covered in fine black fur. Golden cat ears poked through her bushy hair. Long whiskers twitched beside a flattened nose.
"Oh no..." Ron gasped.
Hermione tried to speak.
"I... I think..."
Only a strange meow escaped her lips. Ron immediately rushed to support her.
"We need Madam Pomfrey."
Harry nodded automatically. Neither of them noticed that his eyes drifted, just for an instant, toward the large brass cauldron hidden beneath the broken sink. There was still Polyjuice Potion inside. Not much. But enough.
When they arrived at the hospital wing, Madam Pomfrey looked horrified.
"You put what into your body?"
Hermione lowered her furry head in embarrassment.
"I accidentally used a cat hair..."
"I should think so!"
The matron immediately ushered Hermione toward a private bed.
"I've never seen such careless experimentation."
Ron looked apologetic.
"Will she be alright?"
"In time."
Madam Pomfrey sighed.
"It may take several weeks before every feline feature disappears."
Hermione gave Harry and Ron an embarrassed look.
"Don't... tell anyone."
"We won't," Harry promised.
Ron nodded enthusiastically.
"Never."
Madam Pomfrey dismissed them.
"You two should get back to your dormitories."
As they walked back toward Gryffindor Tower, Ron looked exhausted.
"I don't ever want to drink that stuff again."
Harry kept his eyes forward.
"It was useful."
"It was disgusting."
Harry smiled faintly.
"I suppose."
Ron yawned.
"I'm going to bed."
"You go ahead."
Ron stopped.
"Aren't you coming?"
"In a minute."
"I forgot something."
Ron shrugged.
"Don't stay up too late."
As soon as Ron disappeared around the corner, Harry turned and headed back the way they had come. Moaning Myrtle's bathroom was silent except for the occasional drip of water echoing through the cracked pipes. Myrtle herself floated lazily near the ceiling.
"Oh..."
She recognized him immediately.
"You're back."
Harry smiled politely.
"I forgot something."
"You boys always forget something."
She drifted through one of the sinks with an exaggerated sigh. Harry waited until she disappeared into the plumbing. Then he knelt beside the hidden cauldron. The Polyjuice Potion shimmered faintly under the bathroom's dim light. There was more left than he had expected. Enough for several doses. He uncorked many empty glass vials from his satchel. His hands moved carefully. One ladle. Then another.
The thick potion flowed slowly into each bottle, swirling with metallic colors that shifted between bronze, silver and dark green.
Harry sealed each vial tightly. He stared at them. He should destroy them. That was the sensible thing. The mission was over. They no longer needed Polyjuice. He reached toward the nearest sink. His fingers stopped halfway.
Instead, he wrapped each vial in a scrap of cloth and placed them inside an old leather pouch. He crouched beside one of the broken pipes beneath Myrtle's sink. There was a narrow cavity behind loose bricks. Perfect.
He slid the pouch inside. Invisible unless someone knew exactly where to look.As he pushed the final brick back into place, he remained kneeling for several seconds. His reflection shimmered in a puddle on the floor. Harry Potter. Messy black hair. Thin frame. Round glasses. The lightning scar. Completely himself.
Yet he couldn't stop remembering what it had felt like only minutes earlier. The effortless strength. The silence. The strange relief of walking through Hogwarts without whispers following him. Without everyone expecting Harry Potter to solve every mystery.
As Goyle... No one had cared. No one had stared. No one had expected anything. It had been... peaceful. Harry quickly shook the thought away.
"What am I thinking?"
The bathroom gave no answer. Only the slow dripping of water echoed through the empty room. Harry stood, adjusted his glasses, and left the bathroom. Hidden behind the loose bricks, the three small vials waited patiently in the darkness.
Harry waited three days. Three days of classes. Three days of Quidditch practice. Three days of pretending nothing had changed. Yet every now and then, without warning, his mind drifted back to the feeling of being Gregory Goyle.
The weight. The strength. The silence. It wasn't that he wanted to be Goyle. At least, that was what he kept telling himself. He simply wanted to understand why it had felt so... comforting.
Late on Friday evening, after Gryffindor Tower had gone quiet, Harry slipped out beneath his Invisibility Cloak. The castle was almost silent. His footsteps echoed faintly as he descended toward the abandoned girls' bathroom.
Moaning Myrtle wasn't there. Perfect. Harry knelt beside the loose brick beneath the cracked sink. His fingers found the leather pouch exactly where he had hidden it. Inside were several glass vials.
The Polyjuice Potion still shimmered with metallic swirls. He uncorked one. The familiar smell of overcooked cabbage and bitter herbs filled the room.
"This is just curiosity," he whispered.
He drank. Immediately the potion burned all the way down his throat. The sensation returned far faster than he remembered. His stomach tightened. His arms grew heavy. His shoes suddenly felt too small. Harry leaned against the sink as the transformation spread through him.
His chest widened. His shoulders stretched outward. His sleeves crept toward his elbows as thick forearms swelled beneath them. His hands became broad and rough. His neck thickened. His jaw pushed outward with a dull ache. The muscles of his back expanded until his Gryffindor jumper strained against them. His trousers became painfully tight around his thighs.
Then—
Everything stopped. Harry took a slow breath. He looked into the mirror. Gregory Goyle stared back. The broad face. The thick neck. The heavy brow. Dark, cropped hair. He take off his glasses. Perfect eyesight. Harry blinked several times. The world looked strangely... clear. No lenses. No frames. Nothing between him and the castle. He raised one enormous hand to his face.
"My eyes..."
He smiled despite himself.
"I forgot."
Then he looked down. The smile vanished.
His Gryffindor clothes were a disaster. His jumper stretched so tightly across his chest that the seams groaned whenever he breathed. His trousers barely reached his ankles. Every movement threatened to split the fabric.
"I can't leave like this."
After an hour, Harry watched uneasily as his massive fingers slowly narrowed. His shoulders shrank. The oversized clothes slipped awkwardly from his body. Within moments he was Harry Potter once again.
Keeping to the empty corridors, Harry hurried toward Hogwarts' laundry rooms. House-elves worked silently among towering stacks of freshly washed uniforms. Before any of them noticed him, Harry quietly searched through a pile of clothing awaiting repair.
He found exactly what he needed. A plain white shirt several sizes larger than his own. Black trousers with a wide waist. An unused Slytherin uniform neatly folded beside them. He hesitated. The green robes felt surprisingly heavy in his hands.
"This is only practical," he muttered.
He bundled everything under one arm before slipping back into the corridors. He dressed quickly in the larger shirt and trousers. They hung loosely from his slim frame.Then he uncorked a second vial. He stared at it for several seconds.
Harry drank. The second transformation came even more smoothly than the first. Almost eagerly. His body expanded into Goyle's once again.
This time there was no panic. Only anticipation. The borrowed clothes stretched comfortably over his larger frame. No seams protested. No fabric threatened to tear.
He studied his reflection. For the first time since drinking the potion...Nothing looked wrong. Only one problem remained. His feet.
Transformed, the borrowed shoes from Gryffindor pinched painfully around his now much larger feet.
"I'll need Goyle's."
Crossing into the Slytherin dungeon felt strangely natural. No portraits questioned him. No ghosts paid him any attention. Students barely glanced his way. To them, Gregory Goyle had simply returned after wandering the castle.
Harry entered the boys' dormitory with surprising confidence. Crabbe was lying on his bed, lazily reading a Quidditch magazine.
"There you are," Crabbe grunted.
"Thought you'd got lost."
Harry gave the simplest answer he could think of.
"Took a while."
Crabbe shrugged.
"Wanted to play Exploding Snap?"
"Maybe later."
Apparently that was enough. Crabbe returned to his magazine without another question. Harry quietly crossed the room until he found another large bed surrounded by untidy belongings. Large boots rested beneath it.
His size. He slipped them on. Perfect. Not merely comfortable— Natural.
As he stood upright again, Harry caught sight of himself in the dormitory mirror.
A tall, broad-shouldered Slytherin boy looked back at him. No scar. No glasses. No famous face. No one stared. No one whispered. No one expected anything extraordinary. For the first time in months... Harry Potter had disappeared. And strangely... He wasn't sure he missed him.
The next week, Harry established a routine. Attend classes. Finish his homework. Visit Hermione in the hospital wing. Wait until the castle had fallen asleep. Then disappear.
The hidden vials beneath Myrtle's sink became part of his nightly ritual. Each time he drank the Polyjuice Potion, the transformation came a little faster. A little smoother. As if his body had begun remembering Gregory Goyle.
Harry no longer counted the hours. He counted the evenings. One evening became three. Three became six. Soon, slipping into Goyle's body felt almost as ordinary as putting on a different set of robes.
He no longer gasped as his shoulders broadened. He no longer stared in disbelief when his glasses became unnecessary. Instead, he calmly folded them into his pocket before the transformation had even finished.
"My eyesight..."
He smiled.
"...still perfect."
The novelty should have faded. Instead, it became one of the things he missed most whenever the potion wore off. Life inside Slytherin House proved strangely uncomplicated. Crabbe never asked difficult questions. Malfoy expected little more than agreement. The older students barely acknowledged Goyle unless they needed someone to carry books, move furniture, or stand nearby looking intimidating.
Harry discovered something unexpected. Being underestimated was peaceful. No professors watched him suspiciously. No portraits whispered his name. Nobody wondered if he was the Heir of Slytherin. When he walked through the dungeon corridors, he was invisible in the best possible way. Not because of magic. Because nobody cared.
Meanwhile, Harry Potter still existed. He attended Gryffindor classes every morning.He laughed with Ron. He brought Hermione books from the library.
But something felt... Different. One afternoon, while changing after Quidditch practice, Harry paused. His school trousers felt tighter than usual. He frowned.
"That's odd."
He had always been lean. Now his thighs filled the fabric more noticeably. His shoulders also seemed a little broader beneath his shirt. Nothing dramatic. Nothing anyone else would notice. Probably. He blamed Quidditch.
The changes continued. Every morning after a night spent as Goyle, Harry noticed something new.His palms seemed slightly larger. His grip stronger. His appetite greater. He found himself reaching automatically for second helpings at breakfast. Then third. Ron looked up from his plate.
"Hungry today?"
Harry blinked.
"I suppose I am."
Ron laughed.
"Brilliant. More bacon for you means less for Fred."
Harry smiled faintly. He hadn't realised he'd already finished nearly everything on his plate. Three days later, Harry caught himself standing before the mirror in the Gryffindor dormitory. He rolled up his sleeves.
His forearms looked thicker. Not muscular. Simply... Heavier. His hands seemed broader than he remembered. The differences were tiny. Almost impossible to measure. But Harry knew his own body. Something was changing. He whispered the thought aloud.
"It can't be the Polyjuice."
The potion wasn't supposed to leave permanent effects. Was it?
Hermione remained confined to the hospital wing. The cat-like features had faded considerably, but traces still lingered around her eyes and ears. Madam Pomfrey insisted she stay for observation. Harry visited every evening. Hermione always asked the same question.
"Everything alright?"
Harry always smiled.
"Everything's fine."
She believed him. Or perhaps she wanted to. Ron usually did most of the talking anyway, describing Quidditch practice and lessons while Harry remained unusually quiet.
Hermione noticed.
"You seem tired."
"Just sleeping badly."
Another lie. One that became easier each day. One evening, after leaving the hospital wing, Harry returned to Myrtle's bathroom. He uncorked another vial. Only a few remained now. The potion swirled lazily inside the glass.
"You should stop."
The voice surprised him. Myrtle floated upside down near the ceiling, watching him.
"You keep coming back."
Harry looked away.
"It's only until they're gone."
Myrtle tilted her head.
"Is that really why?"
Harry didn't answer. He drank. The familiar warmth spread through him. His body expanded with remarkable ease. His shirt tightened. His chest broadened. His neck thickened. His glasses slipped from his face before he casually caught them in one large hand. He smiled without thinking.
It no longer hurt. It simply... Fit. Nearly two hours later, Harry waited for the potion to wear off. He sat alone on the bathroom floor. The change began gently. His heavy muscles softened.His height decreased. His jaw narrowed. His glasses returned to his face. When the transformation ended, Harry remained seated.He stared at his hands. They were Harry's hands again.
Yet... Not completely.
His fingers still looked slightly broader than before. The sleeves of his Gryffindor jumper hugged his forearms more closely than they had a week ago. He stood. His shirt pulled faintly across his shoulders. Harry frowned.
"That's impossible."
He looked into the cracked mirror. Harry Potter looked back. Messy black hair. Round glasses. Green eyes. The lightning scar. But there was something undeniably different. His face appeared a little fuller. His jaw just slightly squarer. His frame no longer looked quite as slight as it once had. The potion had ended. Yet Gregory Goyle had not disappeared completely.
For the first time, Harry wondered whether part of the transformation had decided to stay.
The changes were no longer easy to ignore. Harry had stopped timing the Polyjuice Potion altogether. Some nights it lasted two hours. Others, nearly four.
There was no pattern anymore. The transformations came quickly, and the return to his own body had become frustratingly unpredictable.
Each time he waited for the familiar warmth to fade...it lingered.
Hermione had finally left the hospital wing. The last traces of feline features had disappeared, and Madam Pomfrey had reluctantly declared her fit to return to classes.
"You've been quiet lately," Hermione observed over breakfast.
Harry shrugged.
"Just tired."
Ron nodded.
"He's been exhausted for weeks."
Hermione frowned.
"You're sleeping enough?"
Harry forced a smile.
"I'll be fine."
She wasn't convinced.
That evening Harry became Goyle once again. The transformation felt almost effortless now. His shoulders broadened. His neck thickened. His hands swelled until they completely filled the sleeves of the Slytherin uniform.
His glasses came off almost automatically. He slipped them into his pocket without even thinking. Perfect vision greeted him again. He spent several peaceful hours in the Slytherin common room. Malfoy complained about Lockart's homework. Crabbe absent-mindedly demolished an entire plate of pastries. Nobody expected Harry Potter to answer difficult questions. Nobody asked him to make decisions. Nobody watched him. Harry simply existed.
It was... restful. Near midnight he quietly slipped away. He expected the potion to fade before reaching Gryffindor Tower. It didn't.
By the time he whispered the password to the Fat Lady beneath his Invisibility Cloak, Gregory Goyle was still staring back whenever he caught his reflection in dark windows.
Harry frowned.
"That's never happened before."
The portrait swung open. The common room was silent. Only dying embers glowed inside the fireplace. Every armchair stood empty. He crossed the room slowly, listening to the steady ticking of the grandfather clock. No footsteps. No voices.
Everyone was asleep. Instead of climbing directly toward the boys' dormitory, Harry turned toward the adjoining washroom.
Moonlight filtered through the tall windows, reflecting across the polished stone floor. A long mirror stretched along one wall. Harry stopped in front of it . For several moments, he simply looked.
Gregory Goyle looked back. The broad shoulders. The heavy chest. The square jaw. The thick neck disappearing into the collar of his robes.
Harry slowly removed the robe and folded it over a nearby bench. Then the green tie. Then the white shirt. Standing in nothing more than his trousers, he studied himself with quiet concentration. His chest rose and fell steadily. He lifted one heavy arm, turning it slowly beneath the pale moonlight. His forearm looked thick enough to dwarf Harry Potter's. He flexed his hand experimentally. The broad fingers closed into a powerful fist.
"It still feels..."
He searched for the right word.
"...natural."
He turned sideways. The reflection showed a solid frame that occupied far more space than his own ever had. He rested a hand against his shoulder, then traced the line of his arm with quiet curiosity, as though committing every detail to memory.
He expected the transformation to begin fading. Nothing happened.
A floorboard creaked behind him. Harry froze. Someone had entered the washroom.
He turned sharply. Ron Weasley stood in the doorway, barefoot, rubbing sleep from his eyes.
For a heartbeat, neither of them moved. Ron stared. His expression shifted from confusion...to disbelief.
"Goyle?"
Harry instinctively took one step backward.
"No..."
Ron narrowed his eyes. Then recognition slowly dawned.
"Harry?"
Silence. Ron looked from the folded Gryffindor clothes on the bench...to Harry's glasses resting beside the sink...then back to Goyle's face. His own face went pale.
"What are you doing?"
Harry opened his mouth. Nothing came out. Ron glanced at the mirror.
"You were just standing there..."
His voice became quieter.
"...looking at yourself."
"I was waiting for it to wear off."
Ron frowned.
"It's been hours that you deasapear."
"I know."
Harry looked down at his large hands.
"It should have ended."
"But it hasn't."
Ron stepped closer.
"How many times have you done this?"
Harry hesitated.
"I don't know."
"You don't know?"
"I stopped counting."
Ron stared at him in horrified silence. Harry answered so naturally that he barely noticed what he had said. Ron did. The words lingered between them. Neither spoke for several seconds. Finally Ron whispered,
"We need to tell Hermione."
Harry immediately shook his head.
"No."
"Harry—"
"No."
His answer came faster than intended. Too sharp. Too defensive. Ron blinked.
"You've been hiding this from us."
Harry lowered his gaze.
"I wasn't ready."
Ron looked once more at the mirror, where Gregory Goyle still stood despite the passing hours. For the first time since the Chamber of Secrets investigation had begun, Ron felt something he had never expected to feel toward his best friend. Not confusion. Not anger. Fear. Because the Polyjuice Potion should have worn off long ago. And yet Harry was still looking back from the mirror with Gregory Goyle's face.
Harry's transformation finally broke just before dawn. He was halfway back to his bed when the familiar warmth suddenly vanished. His shoulders narrowed. His heavy muscles softened. His jaw drew inward. The weight disappeared from his limbs.
A moment later, Harry Potter stood in the empty corridor once more, breathing hard as his glasses slipped back onto his face. Ron let out a long breath.
"Thank Merlin..."
Harry looked down at his own hands. Thin again. Smaller. Fragile. He didn't share Ron's relief. The following morning, Ron insisted on speaking with Hermione. The three of them met in an unused classroom after dinner. Hermione listened without interrupting while Ron described everything he had seen.
"...he was just standing there," Ron finished quietly.
Hermione's face slowly lost its colour.
"That's impossible."
"I know."
"The Polyjuice Potion should never last that long."
"It did."
Silence settled over the room.
Finally Hermione spoke.
"Harry..."
He avoided her eyes.
"How many doses?"
"I don't know."
"You truly don't know?"
"I stopped counting."
Hermione closed her eyes briefly.
"I was afraid you'd say that."
She began searching every book she could find on advanced potion theory. Three evenings later she spread several heavy volumes across a library table.
"I've found references to prolonged magical adaptations."
Harry looked up.
"But?"
Hermione hesitated.
"Not with Polyjuice."
Ron frowned.
"What does that mean?"
"It means nobody has ever recorded someone taking it this often."
She turned another page.
"The potion imitates another person's body."
Harry nodded.
"I know."
Hermione looked directly at him.
"But repeated exposure might encourage the body to remain in that borrowed form longer each time."
Ron swallowed.
"And eventually?"
Hermione didn't answer immediately.
Finally she whispered,
"I don't know."
From that day onward, Ron and Hermione watched Harry constantly. Whenever classes ended, one of them stayed with him. Whenever Harry disappeared for too long, Ron searched the castle. Hermione quietly inspected Myrtle's bathroom more than once. Harry said nothing. He simply waited. Waited for an opportunity. Waited for them to become distracted.
He thought about the final vial every day. Sometimes every hour.
Several classmates casually remarked that Quidditch training seemed to be "bulking him up."
Harry knew better.
Every morning he compared himself with his reflection. He missed feeling Goyle's fuller shape.
"You have to stop."
Hermione's voice was firm. They stood once again inside Myrtle's bathroom. Ron had discovered the hidden pouch. Only one glass vial remained. Hermione held it tightly.
"I'm serious."
Harry stared at it.
"You don't understand."
"No."
Her voice shook.
"I understand perfectly."
She lifted the bottle.
"This has gone too far."
Harry took a slow step forward.
"Give it back."
"No."
"It belongs to me."
Harry's expression hardened.
Ron stepped between them.
"Harry..."
He raised both hands.
"Listen to her."
Harry's jaw clenched.
"Weasley."
Ron blinked. Harry had never called him that before.
"What?"
"Stop pissing me off! Weasley."
The name came again. Cold. Dismissive. Almost contemptuous.
"Move."
Ron stared at him. Hermione looked horrified.
"Harry..."
He didn't even seem to hear her. She took another cautious step.
"Harry, please."
His eyes turned toward her. For an instant they looked unfamiliar.
"Tired of lecturing everyone?"
She froze. Then came the words neither Ron nor Hermione ever imagined hearing from him.
"Give me the bottle, Mudblood."
The silence that followed was absolute. Harry himself looked startled for half a heartbeat. As though some distant part of him had recognised what he had just said.Then the hesitation disappeared.
He snatched the vial from Hermione's hand. Ron lunged forward.
"Harry, don't—"
Too late. Harry uncorked it. The remaining Polyjuice Potion disappeared in a single swallow. The transformation exploded through him.
Unlike every previous dose, there was no struggle. No pain.No resistance. His body welcomed it. His shoulders expanded with effortless certainty. His chest broadened.
His neck thickened. His face settled naturally into Gregory Goyle's familiar features. His eyesight sharpened before he even remembered removing his glasses.
They slipped from his fingers onto the stone floor. Neither Harry nor Ron bent to retrieve them. The silence lasted several long seconds. Then... Nothing.
No lingering warmth. No expectation that the magic would fade. Only stillness. Gregory Goyle took one slow breath. He flexed his broad fingers. Ran one hand across his heavy jaw. Touched his thick neck. Rested both hands against his broad chest.
Everything felt... Right. He turned toward the mirror. The reflection felt utterly familiar. Not borrowed. Not temporary. He smiled faintly. As though recognizing an old friend.
"So..."
His deeper voice was calm.
"...this is me."
Ron stared in horror.
"Harry..."
No answer. Hermione whispered,
"The transformation..."
Her voice broke.
Gregory looked at them both with quiet detachment. There was no anger on his face anymore. Only certainty. He picked up the neatly folded Slytherin robes. One piece at a time, he dressed himself.
The robes settled comfortably across his broad shoulders. The green tie sat perfectly beneath his thick neck. He slipped his feet into Goyle's shoes. Every movement felt instinctive.
He glanced once toward Harry's abandoned glasses lying on the floor.
For a moment... He searched his memory. They seemed strangely familiar. Then even that feeling drifted away. Without another word, he turned and walked out of the bathroom.
Ron took one desperate step after him.
"Harry!"
Gregory paused only briefly. Without looking back, he replied,
"My name is Goyle."
Then he continued down the dungeon corridors. When he entered the Slytherin common room, no one reacted with surprise. Crabbe merely looked up from a game of Exploding Snap.
"There you are."
Gregory nodded.
"Yeah."
Malfoy barely glanced in his direction.
"About time."
Gregory sat down beside them. The chair creaked beneath his weight. He smiled to himself. For reasons he could no longer explain... It felt exactly like coming home.
