A/N: Hello! Thanks for checking out my story! This Merlin/Harry Potter crossover came about because I really like the idea that Hogwarts is the same castle that was once Camelot, and I also enjoy time travel shenanigans. Put those two things together and this is what happens. Enjoy!

Disclaimer: Is this thing really necessary? Oh whatever. I don't own anything. Not even clothes. I'm a nudist.

Most children instinctively fear being lost and alone in a strange place. It was thanks mostly to this fact that the staff of Hogwarts School of Witchcraft and Wizardry rarely worried about students wandering alone in the castle at night. Of course, when it came to Harry Potter, the usual rules just didn't apply.

It was a frigid night in December when the boy-who-lived found himself lost deep in the bowels of the castle, wandering through corridors that might not have been seen by human eyes in hundreds of years. Harry had been searching for the Mirror of Erised, hoping to once again kneel on the cold stone floor and gaze at the two people whose smiling faces never failed to make him feel safe and loved. By then he practically knew the way by heart, but late at night Hogwarts has a way of playing tricks on even the most savvy explorers. This deep in the castle there was very little way to tell one stone passageway from another. While poor Harry's mind was occupied with thoughts of his parents, Nicholas Flamel, and his last potions class before the holidays, during which Professor Snape's oily hair had briefly caught fire while he was sneering into Seamus' cauldron, his legs carried him down, down, down, until even the Slytherins' dormitory was far above him. By the time he realized where he was, or rather, where he wasn't, he couldn't remember which way he had come from.

Through the shimmery, translucent fabric of his invisibility cloak, Harry could see that the corridor extended straight in front of him so far that he couldn't make out where it ended by the light of his wand. He turned to look behind him but the passageway appeared so much the same that he might as well have been looking in the same direction as before.

Harry's palms began to sweat and he wiped them reflexively on his trousers. He tried to fight his childish instinct to panic and reminded himself that the sorting hat must have put him in Gryffindor for a reason. And besides, in his eleven years he had already known terrors much greater than this. Being lost was nothing compared to facing a fully-grown mountain troll. At least that's what Harry told himself.

He chose a direction at random and walked for what felt like an hour before an end to the corridor finally emerged from the heavy darkness. Five feet in front of Harry was a large stone door, hewn from the same type of rock that formed the passageway. It was simple, yet foreboding, and looked as if it had never been opened, or perhaps was never meant to be opened. There was a symbol carved into the door that Harry had never seen before. It was a shape made up of three spirals connected in the center. Harry was terrified of what he might find on the other side of the door, remembering well the incident with Fluffy in the third-floor corridor, but his curiosity got the better of him. There was no door knob or handle, so Harry pushed the door with all his strength until it finally scraped free of its frame with a horrible screeching sound and swung inwards. Holding his wand at the ready and fully prepared to give any creature he might find a face full of Alohomora, Harry proceeded cautiously.

He found himself in an enormous chamber with walls in the shape of a hexagon. There were muggle paintings of a great city with a magnificent castle and of knights in the midst of a fierce battle mounted on all of the walls. Harry eyes became transfixed when he saw the table in the center of the chamber. It was a round table made of dark oak with a golden dragon carved into its center, and looked to Harry to be ancient. He could almost sense a type of magic emanating from it, as if it carried with it the essence of everything it had borne witness to. Around the table were close to thirty chairs with high, regal backs. A thick layer of dust covered every surface. As Harry stepped wide-eyed and trembling into the room, the stone door slammed shut behind him and six torches, one mounted on each wall, burst into life. Harry threw off the invisibility cloak and ran back to the door at once, but try as he might, no amount of physical force and none of his meager magic could force the door open again. After he'd exhausted himself from trying, Harry felt sure that he'd gotten himself in too deep this time. He would never see his friends again, never study magic, never play another game of quidditch. It was probably close to four in the morning now, and soon Ron and Hermione would discover he was missing. He wondered what they would think had happened to him. If he were there he would tell them to look for his body in Snape's supply cupboard. He pushed his fringe back and messed up his already messy hair in frustration and sank onto the ground in front of the immovable door.

Then, he noticed something he had missed before. On the opposite wall of the chamber was another door, so seamlessly set into the wall that Harry could barely distinguish its outline. The same golden dragon symbol from the table was carved onto it.

As Harry watched, the door swung open with a bang.

"Insufferable, arrogant, supercilious, prattish, pig-headed clotpole…."

Several servants looked at Merlin in confusion as he stormed past them. He didn't give a damn what they thought. Arthur was being a complete ass and he wanted everyone to know it.

In his fit of pique Merlin passed right by Gwen without seeing her.

"Merlin!" she called after him.

"I'm sorry, Gwen, I don't have time to talk. I have to scrub the floors of every room beneath the castle!"

"Oh no, what did you do this time?"

"Why does everyone assume that I've done something? He's just being completely unreasonable!"

Gwen sighed. "It's because we know you, Merlin," she said honestly.

Merlin stopped to consider this for a moment. "Well, I may have made one little mistake," he admitted. Gwen raised her eyebrows at him imploringly. "I, uh, might have accidentally washed all of his white shirts together with his red cape."

"Merlin!" Gwen laughed and put her hand on his shoulder. "Honestly, you're lucky he didn't put you in the stocks for the rest of your life!"

"I'd rather the stocks than scrubbing floors for the rest of my life," Merlin grumbled, glaring at the bucket of water and rag in his hand.

"Come on, it won't really take you that long. Would you like me to help you?" She said it teasingly, but Merlin knew that her offer to help was real. Gwen could always be counted on to help a friend out of a tough situation, self-inflicted or not.

"Thanks, Gwen, but if Arthur found out he would probably have me hanged."

Gwen smiled at him sympathetically and reached into the woven basket on her arm. "Here," she said, handing him a bar of lye soap, "At least take this with you. It will make the work go faster."

"Thank you, Gwen. I'd better get started."

Merlin descended the long and seldom used stairs to the lower parts of the castle, adjacent to the dungeons. Like the stairway to Kilgharrah's cave, the stairs were lit by evenly spaced torches on the walls. When he finally reached the endless bottom floor, Merlin set down his bucket of water and soap and resigned himself to the inevitable. If he tried to do this by hand, it really would take the rest of his life. It was at times like these that Merlin truly appreciated his gifts, despite the threat of discovery constantly hanging over him. He just needed to think of the right spell and he could use the countless hours he would have spent scrubbing doing something far more productive, like protecting the prince's royal behind.

Merlin remembered reading about a spell in his magic book that could remove all dirt from a large area, but he couldn't remember exactly what the words were.

He paced back and forth for so long that the filthy floor looked a bit cleaner under his feet. "Aha!" he said when he finally remembered the spell. He glanced quickly over his shoulder to make sure no one was coming down the stairs who would be able to see him.

"Aliese duru rýne!" As soon as he said it Merlin knew that it was the wrong spell. As his eyes burned gold, Merlin heard a loud bang from somewhere farther down the passageway.

He winced and ran towards the sound. He hated it when that happened.

At the end of a long hallway, Merlin saw that a massive stone door had been flung open. He seldom ventured down this far into the castle and had never noticed it before. He recognized the symbol etched into it as that of the Druids and his curiosity was piqued. He flattened himself against the hallway and peered around the doorway tentatively.

"Aaagh!"

Merlin's eyes were assaulted by a blinding flash of light that suddenly illuminated the previously dimly lit chamber. He stumbled backwards with his hand over his eyes and tripped over his own feet, landing bum-first on the hard stone floor.

"Who's there?" shouted a small voice from the newly bright room.

Merlin scrambled back to his feet and stepped forward, squinting into the white light. "Um...hello?"

A young boy who looked to be about 10 or 11 lowered a stick that was lit at one end and peered up at Merlin's befuddled face. "Who are you?" the boy asked, "And what are you doing down here in the middle of the night?"

Merlin just looked more confused. "What do you mean? It's barely past breakfast." Merlin wondered with some concern just how long this boy had been locked in that room.

"What? It's four in the morning!"

Merlin was growing even more concerned. "Look, maybe you'd better come with me to see the physician. I think you're confused."

"No, no, I don't need to go to the hospital wing. Can you just tell me how to get back to the Gryffindor common room please?"

"The griffin...what?" Merlin was completely nonplussed. "What are you…" But Merlin had just looked closely at the stick in the boy's hand for the first time and it made the words climb back up into his throat. It definitely wasn't a torch. "Are you doing magic?" He gasped out in a horrified whisper.

"Uhh, yeah," the boy said, glancing at his still lit wand. "Any reason I shouldn't be?"

Merlin gaped at him and opened and closed his mouth like a fish for a moment. "I'd say execution is a pretty good reason not to be doing magic, yeah."

"I'm sorry? Look, I really don't have time for this. Can you help me or not?"

Merlin's felt a wave of sympathy for the young boy who was obviously lost and confused, and he kneeled to be at eye level with him. He knew that if he didn't help the young sorcerer, no one else would. "What's your name?" he asked kindly.

"Harry," the boy replied.

"Nice to meet you Harry, I'm Merlin."

Harry's eyebrows bunched together. "Like the old wizard with the talking owl in that muggle movie?"

Merlin had no idea how to decipher the second half of that sentence, so he stuck with the first. "Do you know a wizard named Merlin?"

"Err, yeah," Harry said. "He's famous."

"Huh." Merlin was quite surprised to hear that he shared his name with a famous wizard. It seemed an odd coincidence. He couldn't recall ever having met another Merlin. In fact, he had been a bit embarrassed as a child when he learned that Hunith had named him after a bird.

"Where do you live anyway?" Merlin asked, "And where are your parents?"

"They're dead," Harry confessed in a flat voice. "And I live here, of course, in the castle. I'm in Gryffindor house."

"Gryffindor..." Merlin said slowly. He thought that might have been the name of a noble family. It seemed like those old-blood families were always named after some kind of magical creature. But he couldn't imagine any noble family in which magic had been passed down to be allowed to live in the castle of Camelot.

"Well how did you manage to get stuck behind that door?" Merlin asked.

"I came through that door," Harry said, pointing behind him to the large stone door on the other side of the room, "and it slammed shut behind me."

Merlin looked past Harry and fully took in the massive room behind him for the first time. He couldn't imagine how he had missed it before. It was dimly lit by torches, their light reflecting on the polished wooden surface of the round table. Merlin walked past Harry and into the room cautiously, and the door promptly slammed shut behind him.

Merlin swore under his breath and tried to push the door back open with all of his weight pressed against it, but he might as well have blown on it for all the good it did. He ran his fingers through his hair in frustration and then smirked when he looked back at Harry and noticed that his messy black hair looked like it had received some rough treatment as well. Harry just shrugged at him helplessly so Merlin turned to survey the rest of the room.

He approached the table and brushed it with his hand, struck suddenly by a feeling of...nostalgia? But that couldn't be right, he had never seen this table before. Nevertheless, the feeling of the smooth wood beneath his fingers made him feel oddly wistful.

He shook his head to clear it and approached the door opposite the one which had just slammed shut. Its rough stone surface was engraved with what looked like a family crest with a lion, an eagle, a snake, and a badger on it. He wondered if this was the crest of the Gryffindor house Harry said he was from. Merlin shifted his weight onto his heels and tentatively reached out a hand to touch the door. He pushed it quickly and jumped back as if he expected it to explode. The door glided open swiftly and obediently and Merlin relaxed when he saw nothing but dark hallway beyond it.

Harry let out a soft noise of surprise. "But why wouldn't it open for me?" he complained a bit sulkily.

"I guess you don't have my impressive upper body strength," Merlin teased lightly, gesturing to his scrawny upper arms.

Harry snorted softly and looked at Merlin in mild bemusement. "But who are you anyway?" he asked. "Are you a member of the staff? You look a bit too old to be a student."

This boy was a riddle. Merlin couldn't remember the last time he felt this confused. "A student of what?" he asked slowly.

"Why, magic of course," Harry said as if it were the most obvious thing in the world.

"Shhh!" Merlin shushed him quickly, looking around as if expecting King Uther to materialize out of thin air. "You really should be more careful about discussing magic with strangers. Don't you know that it's banned?"

"Banned?" Harry exclaimed indignantly. "Of course it's not banned!" Harry was really starting to look annoyed now. "This is a school for magic! Hogwarts School of Witchcraft and Wizardry."

Merlin felt as if he were missing something important here. Although the thought of a school for magic filled him with longing, he couldn't imagine such a place existing anywhere near Uther's realm. "Hogwarts? No, this is Camelot. I really think you should let me take you to see Gaius."

Harry let out a disbelieving chuckle. "You're having me on, aren't you? You really had me going there for a while. You really expect me to believe that your name is Merlin and you're from Camelot? Next you're going to say that you know King Arthur."

"Well, yeah. He's not king yet though. I'm Prince Arthur's manservant."

Harry goggled up at him in shock. Then he laughed giddily and said, "And I suppose you call him Wart."

Merlin wasn't sure if he should dignify that with a response. He thought Harry had better be glad that neither royal was here. He would have been hanged three times over by now.

"Look," said Harry, "I'm not saying I believe you, but if you really are Merlin, can't you help me find my way back to my dormitory with magic or something?"

Merlin felt as if someone had poured a bucket of ice water down his back. "How do you know that I have magic?" he asked hoarsely, feeling very panicked. Had his secret gotten out somehow? What if the whole castle knew?

"Never mind how I know. Don't worry, I'm not going to tell anyone," Harry said placatingly. "Come on, I really need your help. If I don't get back soon I'll be in huge trouble."

Merlin wasn't sure why, but he couldn't help but trust the young boy in front of him, and he had never been one to ignore a plea for help, so he resolved to try his best to help the boy.

"Okay," Merlin agreed, "I'll help you. But I don't think you'll find any dormitories down that way." Merlin pointed down the hallway behind the door with the crest on it.

"Trust me, I know where I'm going," Harry assured him.

"If you're sure," Merlin muttered doubtfully. He glanced back out of the door leading back to the hallway where he had left his bucket. "I know a spell that might help you, but to do it I'll need something from back that way."

"Maybe if we both try the door?" Harry suggested. Merlin nodded in agreement, but he wasn't too optimistic that it would work.

The wizard and the warlock approached the door and pushed hard against it. It swung open immediately and Harry and Merlin both stumbled forward into the hallway, having overestimated how much force they would need. "Now who's the weakling?" Harry pointed out a bit smugly.

"It must have been stuck or something." Merlin shrugged at Harry, who grinned back.

Merlin turned and jogged out of the room and down the hallway until he found his abandoned cleaning bucket. He reminded himself firmly to look up the correct cleaning spell in his magic book just as soon as he had helped Harry. It really wouldn't do to keep trying random spells. Who knew how many other mad young wizards were hiding behind all of these doors.

He picked up the bar of lye soap that Gwen had given him, dropped it, and picked it up again before running back to where Harry was waiting for him, tapping his foot impatiently. He looked at the bar of soap in Merlin's hands dubiously and Merlin felt a bit silly. Oh well, he thought, it would work.

Merlin held the soap near his mouth and whispered, "Bebiede þe arisan ealdu, astrye Harry!" The dull yellow bar began to glow an ethereal blue color.

When Merlin looked up again Harry was staring at him with an awed expression.

"Cool," he said appreciatively, and Merlin grinned bashfully.

Merlin handed the soap to Harry, who looked confused. "You just have to tell it where you want to go and it will guide you there."

Harry looked impressed. "That's a neat trick," he said. "Do you think you could teach it to me sometime?"

"Yeah, I'd like that," Merlin said with a happy smile, imagining Harry as a sort of apprentice, even though Merlin barely knew enough magic to be out of apprenticeship himself. "If you ever find yourself in Camelot, Harry, just look for me in Gaius' chambers."

"Right, thanks Merlin." Harry smiled up at him and laughed as if what he had said had been funny somehow. "See you around."

He held the soap up to his mouth and whispered, "Gryffindor common room." The glowing soup slipped out of his hand suddenly and slid out the doorway through which Harry had come, leaving a glowing trail of suds behind it as Harry sprinted to keep up with it, barely remembering to scoop up his invisibility cloak in one hand as he ran. The door swung shut behind him softly.

Merlin saw that the trail began to disappear as soon as Harry had left. Interesting. He had never tried that spell on soap before. He snickered quietly. Oh, he could not wait to tell Gaius about this one.