Title: Harry Potter and the Return of Merlin

Fandom: Merlin/Harry Potter Crossover

Rating: T for slight violence and language

Pairings: Harry/Ginny, Ron/Hermione...or at least the precursors to the relationships

Spoilers: HP - definitely through the end of OotP, since Merlin is supposed to know more than most, there may be other spoilers as well. Merlin - through the end of season 3 because I haven't had a chance to watch season 4, so I can't spoil it, lol.

Warnings: AU. Slight Violence and language.

Beta: the wonderful animeloveramy. I don't know what I'd do without her.

Disclaimer: I do not own Harry Potter or Merlin. They belong to J.K. Rowling and BBC respectively. They have simply been kind enough to allow dreamers like me to indulge in fantasies involving their characters. Some of the text is directly from, very close to, or inspired by what J.K. Rowling originally wrote. This is simply because this fic closely follows OotP and I see no reason to pretend that I'm better than J.K. Rowling and try to rewrite it. I will try to leave an AN at the bottom when I use large amounts of the text.

Summary: The moment Voldemort regained his body, the Old Religion cried out. For the first time in more than a thousand years, Merlin is called from the forward to right the balance once more. Disguised as a fifth year student, he must fight to stop Voldemort when it is not his destiny to do so.

Author's Note: This chapter has been edited for flow and grammar issues and has been reposted.

Prologue: Destiny Calls

Being immortal is bloody annoying, Merlin decided one day about twelve hundred years into his existence, after a ripple in the fabric of magic had knocked him flat on his back. Groaning softly and sitting up, he ran a hand through his hair as he tried to calm his nerves enough so that he could rebuild the mental barriers he hadn't used in over a millennia. When Morgana and Mordred had been causing trouble, they'd often used darks spells that caused the same ripple in magic. Back then, his magic had been growing and he'd been protected first by the natural shields of the young and later by shields of his own making. As magic had changed and Old Magic had become less accessible to the average wizard, Merlin had been forced to lower those shields in order to remain attuned to what was going on around him. It had been centuries since he'd even felt the need to think about his old protections. He knew of only one person in this time who might be tampering with Old Magic.

Since the fall of Camelot, Merlin had been forced to do little more than watch the world and guide it from afar, never truly interfering. He had learned quickly that mankind needed to fix its own mistakes without aid from a powerful immortal. Though he still walked the earth, he was no longer truly a part of it. He was a relic from a time long gone.

His patience had been tried sorely over the years. He had never been one to stand by when there were people who needed help. Years by Arthur's side had only strengthened that conviction. Doing nothing went completely against his character. Only the hard earned knowledge that he would be doing more harm than good had kept Merlin from acting.

The past fifty years had been more trying than most because the dark power that rose during that time was stronger than any he'd seen in centuries. Tom Riddle had done what most feared to do. He'd delved into Old Magic, coming closer to the lore and practices of the Old Religion than anyone else had since the days of Camelot. The Old Religion had not been pleased with Riddle's perversions and Merlin had sensed it in his very soul. He hadn't felt so-called to act since Arthur had still been alive.

But something had held him back. The sixth sense at the back of his mind that had always warned him that Arthur was in danger or that something horrific was going to happen to Camelot had told Merlin that it wasn't yet the time to act. Though it had gone against everything he believed it, Merlin had contented himself with merely watching.

Then the Potter family had come into the picture. It had been centuries since Merlin had felt such a connection to someone. James had rather reminded him of Arthur. They'd both been incredible prats before growing into good men. Though Lily had more fire than Gwen, she'd been the sort kind-hearted woman who saw the good in everyone she came across. It had killed Merlin not to help protect them, but he'd taken comfort in the knowledge that they were doing everything they could with the magic of their time to protect themselves.

Or so he'd thought.

As powerful as he was, Merlin couldn't see everything and he was still human, even if he was no longer mortal. He'd been trying too hard to watch everyone, to watch over Remus at the full moon because the man's plight reminded him painfully of Freya and to keep an eye on Sirius, who was reckless at the best of times and downright suicidal when he thought it might help someone else, and all the other members of the Order of the Phoenix, that he didn't notice what was happening right in front of him until it was too late.

Even after almost fifteen years, Merlin still couldn't figure out how he'd missed the switch. It hadn't been until Voldemort swept into Godric's Hollow that Merlin had realized that he had missed something important. He'd arrived just in time to see an explosion tear apart the upper level of the small house. There hadn't even been time to check for survivors before Sirius had arrived. Choking back tears of rage, Merlin had watched Sirius search the rubble until Hagrid showed up and, together, they found Harry.

Things had only gotten worse from there. Dumbledore, assuming that Sirius had been the traitor, had taken it upon himself to do something about keeping Harry out of the "traitor's" hands, thus leaving Sirius with nothing to lose and no one depending on him not to do something stupid. So he'd gone after Pettigrew, the one Marauder that Merlin had never paid much attention to. The fact that he was not the only one to make that mistake had not made him feel any better. Again, the warlock found himself arriving just moments too late to be of any use. He'd heard Pettigrew shout for the street to hear that Sirius was the traitor from around the corner and had arrived on scene just in time to see him transform and run into the sewer. The ministry had been there within seconds, giving Merlin no time to get Sirius someplace safe. He'd been taken away by the aurors and thrown into Azkaban without a trial. Merlin had spent hours cursing the fact that he had absolutely no power within the current government because he was supposed to be long dead.

He had not been in a good mood when, a few days later, he had managed to calm down enough to find out exactly what Dumbledore had done with Harry. Merlin had been seconds away from storming the headmaster's office when he discovered that Harry had been left with his magic-hating relatives. The only thing that had stopped him was that the balance had begun to rectify itself and he no longer had the right to act. That and the fact that he would have had to pause in his shouting to explain that no, he wasn't dead, and yes, he really was Merlin and that would really have taken away from the strength of his rant.

The next ten years had been relatively quiet. Merlin had never really felt settled even as the wizarding world moved on. He knew that Voldemort was still alive and a little digging had allowed him to discover just how Riddle had managed to cheat death. On top of that, the balance still wasn't quite right because he hadn't died when he rightfully should have. Unfortunately, the imbalance hadn't been large enough to allow the warlock to act. Merlin had contented himself with watching over Harry and helping the boy when he could. Usually that meant nudging Vernon Dursley's mind so that he forgot about something magical that Harry had done or magicking the door of Harry's cupboard open so he could sneak out for food. It hadn't been much, but it was more than he'd been able to do in quite some time.

Once Harry had gone to Hogwarts, Merlin had had to be a bit more on his toes. Harry had a knack for attracting trouble and getting himself into danger in an attempt to help people that reminded Merlin strongly of Arthur. It was something Merlin could sympathize with. He'd tried not to help too much as Harry did need to come into his own, but that didn't mean Merlin had completely backed off. He'd still kept a very close eye on Harry. The Old Religion had recoiled angrily every time Voldemort had managed to find some way to attack. Slowly, but surely, the balance of life and death had tipped further, giving Merlin a little more freedom to act.

Over the past year, it had only gotten worse. The Old Magic had been rippling in a way that Merlin hadn't felt in centuries. He'd spent most of year trying to track down the source of the disturbance rather than keeping as close an eye on Harry as Merlin would have liked. It looked like he'd finally found it. He really shouldn't be surprised that Voldemort was behind it again.

With the shielding around his mind firmly in place once more, Merlin clambered to his feet. He still felt a bit dizzy and was stumbling slightly as he made his way across the small room to a basin of water he carried with him wherever he went. It contained water from the Lake of Avalon, which allowed him to scry more accurately than anything else he'd ever come across. Waving his hand over the basin, Merlin whispered a spell in the tongue of the Old Religion. The water went dark and an image appeared. Merlin frowned. He'd expected to see Hogwarts, not this. There was a possibility that he'd gotten the spell wrong, but he doubted it.

He was looking at a graveyard. A dozen black robed figures stood in a circle around a large cauldron and two other figures. The smaller of the two was favoring one leg, clutching his wand in his trembling hand. After fifteen years of watching over him, Merlin would know that figure anywhere. It was Harry. Merlin found himself wishing that he'd gotten the spell wrong, especially when realized just whom Harry was facing.

"Voldemort!" he hissed. "How the bloody hell did he manage to get his body back?"

Merlin muttered another spell under his breath and the scene wound back to just a few moments before he'd felt the ripple in magic. Being able to manipulate time was something he would never cease to be grateful for, no matter how difficult it could be. Merlin watched in absolute horror as Wormtail intoned a spell that made his skin crawl.

"Bone of the father, flesh of the servant, blood of the enemy," Merlin repeated slowly. He'd heard something like that before. "That's Old Magic. He actually succeeding in finding a spell that he could use. It's no wonder I felt that. How in Avalon's name did I not see this before?"

It was only then that Merlin realized just want the ripple had meant. The balance of life and death had been thrown from the precious position it had been in since Voldemort hadn't truly died on that Halloween night. It was even more out of balance than it had been when he first started taking steps to ensure his immortality. The balance had finally tipped so far that something had to be done to right it. As a warlock of the Old Religion, the only warlock of the Old Religion left, Merlin was the only one who could.

With a snap of his fingers Merlin terminated the scrying spell. If he was going to re-enter the wizarding world, he had some work to do. The sooner he could get it done, the better. Summoning his staff from where it had been hidden beneath the bed, Merlin reached within himself and accessed the power he'd left untouched for centuries. He could feel his eyes glow gold as the room disappeared.

Albus Dumbledore rubbed his temples in a vain attempt to abate the headache that was pounding behind his eyes. The situation couldn't get much worse. It had been weeks since the Triwazard Tournament and Fudge still refused to believe that Voldemort was back. He was using the Daily Prophet for a smear campaign against both Dumbledore and Harry so that no one else would believe wither. The Order wasn't making much headway as they were meeting resistance at every turn and he still couldn't find a Defense instructor. Things were truly a mess.

Sighing, the headmaster picked up one of the many pieces of parchment that littered his desk – a request for new brooms for the flying classes – and set to the calming work of running Hogwarts.

He'd barely gotten through more than a few words when a whirlwind suddenly sprang to life in the center of his office. Papers and lightweight objects went flying. The whirlwind disappeared as quickly as it had come, leaving a young man in its wake. He was wearing a long sleeved red shirt, a brown jacket, a blue scarf, and a sheepish expression.

"Sorry about that," he apologized, noticing the mess that surrounded him. "I forgot what a mess that spell usually makes."

"That's quite all right," Dumbledore said calmly, despite being rather alarmed. "Though I must ask how it is that you were able to pass through the wards without breaking them and without alerting me."

If anything, the young man looked even more sheepish. "It wasn't really that difficult," he said. "Which is not to say that they aren't some good wards, because they are. They're actually quite powerful. I simply have quite a bit of experience with far more powerful wards and, frankly, yours aren't any challenge for someone who is versed in Old Magic."

"Old Magic?" repeated Dumbledore, raising one eyebrow.

"Druidic magics," the young man clarified. "The spells and enchantments of the ancients."

The headmaster frowned. "That knowledge has been lost for centuries."

"Indeed it has," the man said with a cheeky grin. "However, I was first learning of magic when the Old Religion was still being practiced. I have more knowledge of the druidic practices than I do of modern magic."

Silence filled the room as Dumbledore blinked in surprise, trying to process what the young man had said. He leaned forward and folded his hands together, leveling a piercing gaze at the stranger."

"I take it that you employed time travel to learn this," he said coolly. "I am intrigued to know what spells you case in order to travel so far into the past and how you managed to do so without causing irreparable damage to time itself."

To Dumbledore's surprise, the young man laughed. "Nothing quite so clever, I'm afraid. No, I was born over twelve hundred years ago. I suppose that I should have introduced myself. Sorry about that. It has been a while since I've been around people as myself." He walked forward and offered his hand to the dumbfounded headmaster, grinning more broadly than before as he did. "Merlin Emrys, High Warlock of the Old Religion, Court Sorcerer of Camelot, and a myriad other rather important, but now mostly pointless, titles. It's a pleasure to meet you, headmaster."

For the first time in his life, Dumbledore was completely at a loss for what to say or do, so he did the only thing that made sense. He shook Merlin's hand.

"I realize that this is probably a shock," Merlin acknowledged. "I do know that I'm supposed to be dead. There are times that I even wish I was. Watching everyone you ever cared about die is not pleasant, but that's beside the point. Simply but, I am so closely bound to magic itself that it will not allow me to die."

That did make sense. Any witch or wizard who'd paid even the slightest bit of attention to history knew that the Merlin of legend had possessed an almost uncanny connection to magic which had allowed him to understand it and manipulate it on a level that no one had ever before or again accomplished. It was not surprising that there were other side effects to that connection.

"I can give you proof if you need it," Merlin said softly, but without reproach.

Dumbledore bowed his head slightly. "I do not wish to offend you. Unfortunately, as compelling as your argument is, it does seem a little far-fetched."

"A fact I am well aware of," sighed Merlin. He thrust his right hand out to his side. His eyes flashed a brilliant gold and a staff appeared in his hand. The staff was intricately carved with runes. A blue stone at the top of the staff was pulsing with power. But that was nothing compared to the power emanating from Merlin. He seemed almost to glow with it. His eyes were such a brilliant gold, they were painful to look at. Yet, Dumbledore still got the impression that Merlin was holding back.

The headmaster nodded slightly. "I am convinced."

Merlin grinned and the glow faded from his eyes. The staff disappeared and he looked strangely normal without it.

"I must ask, why come forward now?"

The warlock abruptly looked tired. He conjured a chair and sat down. "It's difficult to explain. I am bound to Old Magic and that means there are certain things that I must protect. For the past fifty years, ever since Tom Riddle created a certain diary, the balance between life and death has been teetering dangerously. A decade and a half ago, it was very close to becoming so out of balance that I would have had to intervene. Then Voldemort died, or nearly did, and the balance was mostly restored."

He paused and Dumbledore nodded to show that he understood. When it came to the Old Magics, balance was the key. That the headmaster knew. If the balance was upset, the effects could be catastrophic to magic as whole.

"I take it that the balance has been destroyed now that Voldemort has truly returned," Dumbledore concluded.

"He's deliberately defying death and he's doing so by using ancient magic," Merlin said. "For the past twelve centuries, I could do little more than very indirectly effect events. I was mostly bound to inaction so that the world could move forward. As the only living practitioner of the Old Religion, I must now step forward and right the balance. To be honest, it would have fallen to me even in the days of Camelot and I won't deny that I'm thankful for a reason to actually do something. I was not made to watch as others fight."

Dumbledore took a deep breath and leaned back in his chair. "I must say that I am not surprised that Tom dabbled in Old Magic. I am most troubled that he managed to learn so much."

"He actually learned very little," Merlin said with a shrug. "What he did learn is a version of magic that has been twisted by time. That is what makes it so dangerous. He is tampering with things he can't even begin to understand."

"What exactly do you plan to do?" Dumbledore inquired. "You are thought to be dead, after all."

Merlin chuckled under his breath before answering. "I was hoping to pose as a student. Harry will be Voldemort's main target and I would like to be close to him. Something tells me that helping Harry will be the best way to fix this."

"You do not look young enough to be a student," Dumbledore pointed out. "However, I do think that we can pass you off as a young man who was traveling with his parents until their deaths and did not receive an adequate education. It might also be wise to claim that you battled illness as a child and were forced to begin your education late. Though I fear, you may be ridiculed for that."

"Nothing that I have not heard before," Merlin shrugged

"Indeed. I take it you would also like to be apart of Order meetings?"

Merlin suppressed a small smile, obviously not surprised that Dumbledore had assumed that he knew about the Order. "I would rather just be kept up to date. It would be suspicious if a wizard still in school, despite being overage, is part of the Order."

"Very good," the headmaster said in agreement. "How would it be best to contact you?"

To the headmaster's surprise, Fawkes suddenly soared across the room and landed on Merlin's shoulder. The phoenix gently nuzzled his cheek, letting out a quiet, melodic croon.

"I believe we have our answer," Dumbledore said with an amused smile.

Fawkes dipped his head in agreement before fluttering back to his stand.

The two wizards spent the next several hours discussing the various logistics of turning the great Merlin Emrys into Hogwarts student Myrddin Lyonnesse. Albus had given him a list of all the books used through fifth year so that he would be able to more easily pretend to be a student, as well as a bit of a crash course in modern wizarding practices. It appeared that watching the wizarding world wasn't quite enough for him to be able to completely blend in, but Merlin was certain it would be fairly easy to pick up.

It was late by the time Merlin rose to leave the headmaster's office. But before he did, he gave Albus one last piece of advice. "You should tell Harry of the prophecy. This year will be pivotal for him and for all of us. Gaining his trust will be paramount. If he has to search for the answers himself because you would rather him go into this blind, you will lose it."

With another whirlwind, the ancient warlock who looked barely older than a boy disappeared, leaving Albus Dumbledore with a lot to think about.

Upon returning to his home, Merlin waved his hand once, packing all of his belongings into a large trunk that was sitting against the wall. He wasn't that disappointed to be leaving. Despite the years he had spent there, it hadn't been home.

A small, winged figure came soaring out of the bedroom and alighted on his shoulder, just where Fawkes had been not too long before.

"Are you sure of this course of action?" a familiar, ancient voice inquired.

Merlin nodded. "I'm sure, Kilgharrah," he murmured. "There's no other choice. Harry is going to need all the support and help he can get in the coming days. His friends are strong, and will stand beside him. But they have no concept of what they are truly facing. None of them are aware of just how dangerous this is. They need someone to look after them. Besides, I would much rather be in the thick of things. I missed too much the last time because I was detached from the situation. I will not allow that to happen again."

The great dragon, once so much larger than he was now, but no less wise, let out a quiet sigh. "You are correct, young warlock. But be wary. Though your magic is old and powerful, such as no one else on this earth, Voldemort is cunning and his malevolence knows no equal. Do not underestimate him."

"I won't," Merlin vowed. "Too many lives are at stake here."

Kilgharrah chuckled. "You have grown much since first I met you. It has been an honor to be your companion over the centuries."

"I could say the same," Merlin said with a small grin. "Will you accompany me to Hogwarts? It will be a simple matter to cast a glamor so that you appear to be a cat, or some other manner of common creature."

"Must you really ask?" Kilgharrah demanded, sounding just the slightest bit affronted.

Merlin let out quiet laugh. "I thought it better to ask than to assume." He snapped his fingers and the trunk transformed into a leather bracelet that he bound around his wrist.

"What exactly are your plans for the rest of the summer?" Kilgharrah asked. "Surely you don't intend to do nothing."

"Of course not," Merlin scoffed. "I plan on keeping an eye on Harry. He is most vulnerable during the summer months when he is not at school, amongst other sorcerers."

With that, he snapped his fingers and the two remaining remnants of an ancient time found themselves standing on the corner of thoroughly modern and thoroughly anti-magic Privet Drive.

The adventure had finally begun.