As stated in the summary, this is an Alternate Universe fic of The Crystal Cave, Episode Five of Season Three, in which Arthur discovers Merlin's secret. *cue Beethoven's Fifth*
Keep in mind this is just one setting that this could happen; I made it at the Crystal Cave specifically because I like the old sorcerer. He was cool, man.
I hope you enjoy! And excuse errors. I have no beta. Obviously.

Chapter I

Arthur could scarcely breathe.

It was not for the pain that this was so, though there was much of that, certainly, searing in him like white-hot flames; they licked at his back, where he could feel warmth pouring out of him from a hole which seemed the size of a boulder. He knew what that warmth was; it was his life's blood, draining away from him, and he was powerless to stop it. He was powerless to do anything at all, even so much as open his eyes. That did not stop his feeling, however, for though his mind was dull and sluggish with nausea and pain, he was aware of every sensation that took hold of his body. He had even felt it, dimly, when Merlin removed the arrow, unaware as the servant was that his master was screaming in his mind as it slid out of him.

Now, he could feel the fever ravaging him, as the infection began to do its work. He could feel himself shivering, sending more sparks of agony up and down his spine, from the wound to every nerve of his body, and back again.

He was dying. He knew that much.

As he lay there, trapped in his own mind where he knew of nothing outside the fever and agony, he thought to himself how utterly dishonorable it was to die this way. After all he had survived, over all he had been the victor, to be remembered as Prince Arthur of Camelot, son of the feared King Uther, the boy who got lost in the woods, was shot in the back by feeble bandits, and died on the damp forest floor was not something he wished to be written in the records for all future generations.

Gradually, he became aware of other sensations—movement around him. Footsteps, light and quick. Merlin, he realized with a start; he had forgotten the boy was even here with him. Everything seemed so distant now, like he was floating beneath the waves of a deep and dark river, unable to reach the surface for his immobility, and the rest of reality was on the shore, far above him. And getting farther.

There was voice reaching him; the words themselves ran together, muffled, but the gentle rises and falls of the tone were unmistakable.

He wanted to answer, to tell Merlin to stop talking and start helping, but his own voice would not even so much as rise in his chest before dying again.

The sounds started to become closer, louder, and he felt something slick and hot and somewhat disgusting, like marshy leaves during the summertime, press against his forehead. Merlin was treating him, he knew, trying to force away the shock overwhelming his wounded body and make him well again.

More words, barely trembling and hushed. He could understand them, but somehow he still knew that it meant nothing good, that he was not coming back. It was almost as though he was fading away, and all the feelings of pain and sickness dwindling into numbness, so he might hear and feel the world clearly for his last moments of his life.

"Come on." A whisper.

"Dollophead." Louder.

For one second, he craved with every fibre of his being to have mobility of his arm for one last time, so that he might have the pleasure of slapping the back of Merlin's head for calling him a dollophead in his final minutes of life.

A hand, cool and firm, tapping his cheek lightly.

"I need you to recover," Merlin's voice said from somewhere in front of him.

He wished he could say precisely what he wanted to that; what did Merlin think? That he desired for his servant to watch him die?

Idiot, he thought in the most lucid portion of his brain.

Then, there was a silence—a heavy, meditative silence. Even in his present state, he could feel the sudden deepness of Merlin's thoughts, as though the gravity of them radiated from his lean frame in waves. He did not understand it. He had never seen Merlin so grave before; he couldn't even envision his pale face looking as contemplative as the silence gave testament he was.

What was happening? he wondered, slightly panicked. Could his servant see how quickly he was slipping away? Was Merlin choosing whether he should continue to tire himself by treating his master or admit defeat instead, and allow him to perish? Was the thinking of leaving him and returning to Camelot for aid? He knew he would never survive that long all alone….

A dozen possibilities of what would happen thereafter raced each other through his fever-wrought mind. Not one of them had been accurate, as he discovered a moment later.

He felt Merlin's steady hand upon his shoulder, turning him so that he rolled more upon his front. He heard the slight tinkling of his armor as it shifted. Then, the burning hiss of stinging pain once again invaded his consciousness as he felt something warm cover the open wound through his tunic.

A hand. Merlin's hand. He was struggling for lucidity, diminishing as he was so rapidly that he did not even realize he'd already faded considerably into the sweet call of unconsciousness. In his mind, he instinctively clutched onto the feel of the long fingers against his back and willed himself to remain fixed upon it; if he could continue to use Merlin's touch as a means of grounding himself, then perhaps he could retain his strength long enough to fight the battle with his own betraying body.

The fingers flexed, the palm flattening, pushing steadily against his wound. Familiar fires of agony roared when that pressure was applied so forcibly. He was almost grateful for it; the pain kept him aware of his plight. Merlin pushed harder. That was too much, Merlin, he wanted to reprimand, too much pain all at once….It made him wish for the numbness of oblivion….What was Merlin doing?

Then, he was pulled into his former clarity by two strange words—words which shattered everything else in mere seconds and became his only awareness.

"Purhhaele dolgbenn."(1)

And his heart stopped.

It was Merlin's voice. He knew it was. He could identify his servant's voice in a sea of others.

Then again, it…wasn't. Merlin's voice was not so low and controlled, did not sound so very weighty and treacherous. His voice did not have an indescribable, underlying hiss, nor did it raise the hairs on Arthur's neck by its sheer power. More certainly than all, his foolish servant's prattling voice did not recite spells of magic.

That is what this was. He knew it with all his heart and mind. It was magic.

A misinterpretation, he told himself, a hallucination. Product of his fever and pain and fear. Nothing more. Not real, not Merlin….

Then, from another brief silence, while his mind whirled with sickness and confusion,

"Listen to me, clotpole. I don't care if you die; there are plenty of other princes. You're not the only pompous, supercilious, condescending, royal imbecile I could work for. The world is full of them. But…we'll give it one more chance."

Relief. That was the Merlin he knew. That was his Merlin. The mad, honest, sardonic, resolute, gentle Merlin who never disappointed or bored him, who never gave him undue respect for his title alone, who never had given reason at all for Arthur to mistrust him. This was the Merlin who never, never would fall into the wretched black pit of sorcery. Not his Merlin; his Merlin was too wise for that, too strong, too good to be defiled by it.

He felt the horror drain from him, and his mind eased as he felt Merlin touch him again; he welcomed the touch, for this was Merlin, and Merlin was not leaving him, and Merlin was all the pure and blameless boy he had always been. Perhaps that was why Arthur had grown so very fond of him. The world changed, became darker, colder, different…but Merlin never did. Merlin was the one constant he had in a circle of shifting shadows and cutting lies. He was untouched by evil, guided always by his selflessness and compassion, untainted by greed or hate or any of the iniquities of the rest of mankind.

Merlin was his only faithful light. Even now, at the end of everything, when nothing else remained but the darkness closing in around him, Merlin was there with him, as he had always been since the day of their meeting, never failing, never changing.

Merlin spoke again, wrenching Arthur from his mind's wanderings and back into reality. The words which reached him were no more ones of comfort, or of sorrow, or resolve, as he expected.

His blood ran cold at the horribly grating, fearful snarl which seemed more suitable coming from the throat of a demon of Hell than his faithful and valued servant.

"Licsar gestapol nu!"

So shaken was he, that he could not even form a coherent thought in his mind. All thoughts of comfort and security reversed, he was driven farther into that abysmal darkness than he had ever been.

There was no denying it now. Merlin was a sorcerer—an evil, corrupted practitioner of the black arts. Everything Arthur had known, everything he had been trusting so irrevocably for so long, was gone. Merlin, his pure-hearted Merlin, was a liar, and a deceiver of the worst kind. What more was there he did not know? Could Merlin have been responsible for any of the misfortunes that had befallen them over time? The curses and spells and terrors that had come to the Pendragon castle and to Camelot for these years, could they have been product of this guttural, wicked voice arising from his servant's throat?

Any of them could have been Merlin's doing, he realized, and for the first time since he was a child, he wanted only to weep alone in a corner.

Merlin, for all his supposed sincerity and kind understanding and uncomplicated rareness, was no better than the wretched street witch who had tried to kill him at the beginning of their companionship. (2)

Arthur felt sick, and broken, and welcomed the blessed darkness that lured him.

The last thing he knew before all was lost upon him was the feel of Merlin's hand—wet with his own blood—pushing a strand of hair from his damp forehead.

To be continued

(1) I know anyone who writes for Merlin probably needs/would like to know how to write each of his famous spells. Took me a few wrong clicks, but I found a guide for every spell in each show through Season Three for anyone who needs/wants it. h t t p : / / m e r l i n . w i k i a . c o m / w i k i / S p e l l s. (Because of FanFic's ridiculous rules, I had to put a space between each letter/symbol, so just join them together and search it.) You may thank me with reviews.

(2) Reference to The Dragon's Call, Season 1, Episode 1.