A/N: Sherlock is Ravenclaw and John is Hufflepuff. Or whatever house you want! I've had this idea in my head for almost six months and I decided I need to write it down. I would like to do a whole HP AU but I don't have the time now. Please listen to Imagine Dragons 'Radioactive' because that is the song I had in mind while writing this. Thanks! Sherlock's POV

When I wrote this I was totally thinking of the scene with Harry and Sirius in the third movie. My canon is Sherlock is fantastic at Potions because it's like chemistry.

Sherlock's uniform clang to his skin. No matter how fast they ran, the dementors were right at their heels. How long they had been running, Sherlock had lost track of all time; of all reality. It was only him, John and the dementors that had somehow made it onto school grounds.

Where ever they went, the creatures easily followed them. There was no hiding. For the hundredth time that night, Sherlock desperately wished he had a happy memory. Something, anything that would summon a Patronus that could act like a shield.

He was the only one in sixth year that still couldn't properly execute the charm. Even though John could summon one, a single Patronus could do nothing against so many dementors. Because there couldn't just be one- it was a swarm that had descended down onto Hogwarts.

From the first day it had been introduced in class, no matter how hard Sherlock tried, only a spark would erupt from his wand when he spoke the charm. The others had mocked him but John had been oddly silent. If anything his eyes had softened and had focused on something faraway.

John's Patronus was a small hedgehog. The class had laughed until they had seen what it could do. As always John Watson was compact power.

The night was thick and warm. Sherlock's chest stung; his side was starting to hurt and he knew that he couldn't run for much longer. No matter how hard he breathed in, there didn't seem to be enough oxygen filling his lungs. Sherlock didn't have to look at John to know that he was doing much the same.

Time had run out.

The trees suddenly broke and there was a was small lake blocking their path. They stopped short and Sherlock turned to John. The smaller boy was breathing heavy, his entire face red from the physical strain of running.

Before Sherlock could say anything, his breath clung in the air before in a white cloud before him. The warm night air was quickly turning bitting cold. The lake started to freeze over, slowly every inch of the still water cracked and moaned as it turned to ice. Sherlock swung his head from side to side but there were no dementors in sight.

John gasped. Sherlock turned his head and saw that the Hufflepuff was looking up. Sherlock lifted his head to see the dark creatures circling overhead. I thought they were trailing behind. They were above us the whole time.

That was when Sherlock truly knew there was no escape. The creatures would follow them no matter how far or how long they ran. They had to hold their ground and try to force the dementors back. But how? Sherlock gripped his wand tighter and it had never seemed so useless. It might as well have been a twig.

"Expecto Patronum!" John screamed and light erupted from his wand. A hedgehog burst forth and charged as the first dementors swept close to them.

Sherlock lifted his wand and screwed his eyes up in concentration. "Expecto Patronum!" There was a wisp of light and then it faded out. Sherlock cursed. "Expecto Patronum!" It sounded like a sob in his ears.

John held his wand high, "Sherlock! Think!"

He knew what John meant. Think of your happiest memory. No matter how hard or how deep Sherlock searched he could never find it. It wasn't receiving his Hogwarts letter. It wasn't defeating Jim Moriarty in a duel. It wasn't even when he had met John.

Sherlock had never felt so empty. He was the freak. Others had found their memory in a matter of days, for John it had only taken one class. So why was it so hard for him? The one thing that the great Sherlock Holmes couldn't do?

Despite John's best efforts, a dementor got close enough to suck at his face. John screamed as his soul was slowly dragged out of him. Sherlock managed to grab John away from the dementor but his Patronus had already started to flicker.

"John? John!" Sherlock's voice was frantic as he shook the other boy.

John's eyes flickered open and he looked around confused for only a moment. "Expecto Patronum!" The Patronus burst forth and continued to do what it could to protect them.

It was an inevitable. No matter how hard John fought the dementor's would kiss them. Maybe it wasn't so bad. He couldn't find a happy memory, so what did it matter if they took his soul? He had no heart. What would missing a soul matter?

John screamed again. Another dementor had swept close and was breathing in his face, taking out the essence that was his best friend. It should have been enough to spur him. If had been any other spell, he could have mastered it with ease. Expecto Patronum was about searching deep in one's self and reaching out for strong emotions. Happiness. Love. Emotions Sherlock had been told many times that he did not have.

It was a cruel joke. Even with all his skills and knowledge, they were going to die because sentiment was more confusing than any spell or charm. Another dementor glided past them and Sherlock got his first taste of a dementor's kiss.

His heart clinched in his chest. Sherlock had never known it was possible to feel so cold; so empty. Even at his worst, he had never felt like that. Nothing had ever made him so numb, like his entire body had ceased to be.

John's legs gave out and he fell to his knees.

"John!"

Sherlock kneeled next to him. John's eyes were growing dark and the rosy blush that had covered his cheeks was replaced by an ashy gray color. John held his wand up for another moment before it slipped out of his hand and fell to the forest floor without a single sound.

"John!" Sherlock gripped his shoulder and shook. John's eyes were glazed over and unseeing.

"Sherlock-" It was barely above a whisper. John's lips barely moved, "it's so cold."

"John!" Sherlock didn't recognize his own voice as it cracked over the single word.

It couldn't end like this! They were supposed to do so much more! Be so much more! Together, it had always been together. Because Sherlock had never envisioned a future without the Hufflepuff.

What future was there without John? Sherlock shook him even harder but John did not break from his trance. The Ravenclaw's hands clamped onto his head. He dug his fingers into his scalp trying to physically pull out a memory. Had he ever been happy? Had there ever been a time?

His first broom. His parents. His brother! Something! Anything! What's wrong with me?! Sherlock screamed as the tears started to fall from his closed eyes. They stung his cheeks; almost turning to ice as the small drops of water made a path down his face. When had he ever cried? Many times...

...before John.

When there had never been light. John, I thought it would be you! What else could it be other than his best friend? It was only moments until the dementors would crowd in and that would be it. A happy memory! A strong memory! Think!

Sherlock gasped as a hand grabbed a fist full of his robe. John's hand was clinging to him. Something cracked in Sherlock's chest and his hand left his head to cover the smaller boy's tight fist.

It was John. He had just gotten it wrong. His happiest memory wasn't meeting John. He had thought the small Hufflepuff boring and average when they had first met. No, it wasn't then. It was later, when Sherlock had realized that John Watson was so much more.

When John had smiled at him for the first time with genuine glee. When they had shared a laugh and Sherlock had known with certainty for the first time that he wasn't being laughed at but with. When John had made him feel more human than anyone else ever had.

It wasn't John. It was what he experienced when he was with John. When they were together. It was a light switching on and Sherlock finally understood.

John Watson was his happiest memory. Against all that was happening around them, Sherlock closed his eyes and concentrated on the warmth coming from John's hand. The Ravenclaw stilled his mind and for once didn't try and think about his happiest moment, instead he tried to feel his happiest moment.

"You're brilliant!" The small boy exclaimed with a wide smile.

"I'm not doing your homework."

"I'm not asking you too." The Hufflepuff's brow bunched in confusion.

"Then what do you want?" Sherlock pursed his lips.

"I wanted to tell you that you're brilliant. That potion you made was just...well, brilliant." He tilted his head.

"Really?" Sherlock refused to let his voice sound hopeful.

"Yeah." The boy's eyes twinkled.

Sherlock was not blushing. He wasn't.

"I still can't believe the look on Moriarty's face!" Watson's laugher bubbled out of him and he held his stomach as tears sprang up.

"I suppose." A smile started to twitch at the Ravenclaw's face.

"Holmes," Watson smirked.

"He did look rather foolish when his arse skid along the floor of the training hall." Sherlock couldn't believe the words that had just escaped his mouth.

Watson just laughed harder.

"I can't believe we're doing this." John whispered.

Sherlock putting a finger of warning on his lip. They were sneaking into the Potion's classroom. He needed an ingredient for a potion and the Professor had refused to give it to him. John had caught the Ravenclaw sneaking around the halls. Instead of chastising him, John had wanted to tag along.

John's eyes smiled in the dim light, they said 'Don't ever do this without me again.'

Sherlock never did.

"The Yule Ball is the stupidest thing ever!" John huffed as he sat down next to Sherlock under the massive oak beside the Lake.

"I take it Mary said 'no'?" Sherlock refused to be happy that John had been rejected by the other Hufflepuff. He refused.

"She's going with Tom." John tossed his textbooks in front of him. He threw back his head and rested it on the trunk of the oak.

They sat in silence for a few moments. A small fuzziness spread out in Sherlock's chest and he looked out at the Lake. Sherlock glanced over at John. His eyes travelled down his throat and down to the collar of his shirt.

John licked his lips.

"I guess we can be dateless together, yeah?" John turned his head and smiled at him.

"I'm going with Victor." The words left a sticky feeling thick in his throat and they carried no happiness in them. It was a fact. Sherlock turned back to look at the water.

"Oh."

"Why are you here?" John looked up.

Sherlock was in his dress robes. He had escaped the Ball. Without John it had been so empty, even with Victor. Well, the Slytherin had been a distraction but he was no longer an interest to him. Sherlock realized the only reason he had accepted Victor's invitation to the Ball was because he had thought John was going with Mary.

"Boring."

John laughed. He grew oddly quiet for a moment and then averted his eyes. "I'm happy you thought so."

Sherlock nodded and sat down next to the other fifth year. "So..."

"Misery loves company!" John said with a smile that was too big and too forced.

"Are you miserable, John?" Sherlock genuinely wanted to know.

"No, not now. You're here." John's mouth snapped shut. "No, I mean-"

Sherlock smiled. He hadn't even know his face could move in such a manner before he had met John. When Sherlock was with him, it made the other boy happy.

Sherlock made John not miserable.

Sherlock smiled into the sleeve of his dress robe before sliding down to the floor next to John. The fire was warm and Sherlock was finally content.

Sherlock's eyes snapped open. They made each other happy. That was it. The feeling, the memory he had been looking for. It had only happened six months ago. That was why he hadn't realized sooner. The Ravenclaw had thought that the memory had to be old, not so new. It was still so fresh- the moment when he had first known that John was much more than just a friend.

He gripped his wand tighter. "Expecto Patronum!"

Sherlock cleared his mind and only focused on the tightness in his chest. A feeling that he had felt for the first time that night on the Yule Ball. Something he had kept locked away, too afraid to explore what it could mean to him. How it could change his relationship with John. It was a memory laced with trepidation but the joy in it was overpowering.

The tip of the wand exploded with light and Sherlock had to close his eyes against the force of it. Waves of energy erupted out and the entire forest was alight. Sherlock gripped his wand harder. Pulse after pulse rolled out and a dementor let out a toe curling shriek. Another one followed and soon all of the dementors were being forced back by the power of the charm.

Sherlock gripped John's hand tighter. He thrust his wand up higher and strained to power every fiber of his being into the charm. Another burst of white light and an otter was dancing before him. It seemed to swim in the air and it twisted around them playfully.

He was so busy concentrating on the charm that Sherlock missed John's eyes slowly sliding back into focus. John's fingers moved until they were interlaced with Sherlock's slick hand. The Hufflepuff's left hand picked up his wand and then he raised it and yelled out, "Expecto Patronum!"

The hedgehog leapt out of his wand and shuffled over to the otter. It nuzzled up to the other Patronus and rubbed their faces together. They molded around each other and mingled before dashing up and plowing into a dementor- exploding into a ball of white light.

With every pulsating wave of the charm, the dementors were pushed back further and further. He had once thought it impossible to banish one of the horrible creatures. Now no matter how many there were, it didn't seem like a challenge. Because he had found it.

His happiest memory had been beside him the whole time.