Elrond could not say when exactly the evil first arrived to stain his lands. He only knew that, by the time he was able to consciously recognize the terrifyingly subtle feeling wrongness which teased feather-light against the periphery of his senses, it had probably been ghosting around the outermost borders of his lands for weeks, circling like a wolf around the protective haven of a lone traveler's campfire, waiting for the perfect moment to strike. However, once he knew it to be there, his awareness of this interloper, whoever or whatever it might be, chafed at him without respite, like a thousand of the smallest splinters lodged under his skin.
He could not allow such an affront to the sanctity of his protectorate to remain for a moment longer than necessary, not when it was within his power to remove it, so he took a dozen of his finest warriors and rode out to face it head-on. Their plan was simple. They would not try to drive it away, for to do so would merely be to drive it towards those less suited to defend themselves against it. Nor would they try to capture it, for all signs indicated that it was a corruption which longed to spread itself, and they could not allow that to happen. No, they would find it and destroy it with swift steel and cleansing fire, so that it would blight the land no more.
At first, the thing proved difficult to track. This was not merely a creature which could tread lightly upon the ground like a hobbit. Instead, it was something seemingly so immiscible to the natural order that the very earth rejected its touch, refusing to retain signs of its passing, letting it slip through the woods almost as intangibly as a wraith. Lacking visible footsteps, they were forced to follow the trail of death it left in its wake like a trail of breadcrumbs from a children's story. The bloodless bodies of animals, sometimes as small as foxes and rabbits, sometimes as large as deer, once even a full grown wild boar, scattered every mile or two along the way told them that they were going the right way. Large animal or small, the corpses were always the same, killed by a single wound to the throat, made by jaws shaped like that of a human or an elf but with teeth which were far too long or sharp to belong to either. And, gradually, the scenes of death they came across showed signs of being fresher, more recent.
They were catching up.
On the third day, they found a spot which looked as if the creature had dug down and buried itself in the soft loam between the trees. They could only guess as to whether it had either been resting for a time or waiting in ambush for prey which never arrived. It had clawed its way back to the surface and moved on some unknown amount of time earlier in the day. Even as they watched, the dug up earth seemed to minutely shift and resettle itself, smoothing away any sign that it had ever been disturbed as if trying to forget the fell thing which had temporarily dwelled within its unwilling protection. How many other such places might they have passed too late to catch a glimpse of the vanishing evidence of their existence?
A few hours after that, right around sunset, one of their own disappeared. By the time that the faint whiff of old rot drifted in on the breeze to put the party on alert, it was too late and the warrior was already gone without a trace. There had been no cry of alarm, no creaking of armor, not even the rustle of the dry leaves which covered the ground. One moment he had been there, covering the group's left flank and the next moment he was not. After much casting about, they finally found his bloodless body carelessly draped in the highest branches of a tall tree, as if he had been dropped there by some giant bird rather than dragged up the trunk by something humanoid shaped. His mouth hung slack, and his dead eyes were frozen wide open in a look of terror rarely seen on the face of an elf, especially not on a warrior as battle-hardened as this one had been. The single wound to his throat was the same as all the others.
Whether emboldened by its easy victory over one of its pursuers, empowered by the taste of elf blood, or perhaps both, the creature did not wait long to strike again. Before dawn, another elf, this one a brave warrior by the name of Gaenelduil, who had fought by Elrond's side since before the end of the second age, had disappeared. This time, no amount of searching could produce the body even though the remaining eleven elves combed the woods all day, making full use of their combined many thousands of years' worth of skills. Their scouring of the area for clues was to no avail, as was their attempt to close ranks and prevent any further disappearances.
Within a few hours of night falling again, so had two more warriors, whisked away and slaughtered, all without a sound. Or maybe they had been slaughtered without a sound and then whisked away. There was no way of knowing in which order the events had occurred. There was nothing but a fleeting smell of old blood and a sudden sense of a greater emptiness than before to alert those who remained of the fact that there were now fewer of them than there had been scant moments ago. And just like that, the once proud hunting party of thirteen was down to nine.
By that point, Elrond had reached the conclusion that whatever was capable of eliminating some of the best warriors Middle-Earth had to offer with so little apparent effort was not a force to be trifled with. At the time of the fourth disappearance, the hunters-turned-prey were already in retreat. It was already too late, though. Perhaps it had been too late ever since the moment when Elrond had decided to set out on this quest without bringing along every single one of the scores of warriors then at his disposal. Even now, the thing was toying with them. They found the bodies of the two most recently dispatched warriors waiting for them several miles along their path of retreat.
And then, not long after, it allowed itself to be seen for the first time. She allowed herself to be seen. As the fleeing former hunting party entered a small clearing, she emerged from the woods on the far side, stepping into the moonlight as casually as a great lady entering her home's banquet hall. She must have been an elf once, and to a human's eyes she would have seemed beautiful, even wearing nothing but dirt and tattered rags as she did, for she was still fair of shape.
However, to an elf's keener senses, she was an abomination. Her body was too still, even when she moved. Her skin was flawless, but no heartbeat stirred blood beneath it. She flared her nostrils and scented the air like an animal, but she did not breathe. She was an empty husk devoid of life and spirit, a corpse given will and movement where there should have been none. An orc would have been less repugnant to behold, and Elrond did not need to look to his fellows in order to know that they all felt the same. Even had he wanted to look to his fellows, he could not risk taking his eyes away from their newly revealed foe.
As if reading his thoughts, the creature smiled impossibly wide, showing off teeth which were far too long and too sharp. Then she turned her head and looked back over her shoulder. A moment later, another abomination stepped out of the woods to join her. This one too had once been an elf. This one had once been Gaenelduil.
Someone in their group let out a howl of rage, and grief, and despair. Perhaps they all did. Then, both sides rushed at the other, and the battle was met. The nameless former elf woman and the thing which had once been Gaenelduil were both impossibly strong and fast, dealing terrible damage wherever they struck, even though they used no weapons but their rending hands and gnashing teeth. They tore through the party's armor like paper, and even what should have been mortal wounds barely slowed them down.
Elrond and his party did not go meekly like lambs to the slaughter, though. They were all seasoned warriors, and now that they could see their foes, they could work together against them. Any elven fighting unit, even one so recently harried as this one, was more formidable than the sum of its parts. It was an epic battle for such a small number of participants.
The two sides fought for nearly an hour before someone managed to pin Gaenelduil's body to the ground with a broken tree branch through the heart and then separate his head from his shoulders, at which point the mockery of life finally left his corpse, and he did not rise again. By then, only Elrond and three of his companions remained alive, and one of those, Tareldir, had been hamstrung in both legs. Elrond himself was bleeding from a half dozen places and was not sure he would live much longer, and the two other elves still capable of standing looked little better, but they once again had hope, because they finally knew how to kill these things.
The three made one final rush against the remaining creature. She was stronger and faster than the thing wearing Gaenelduil had been, but many times during the course of the battle the elves had managed to give her what should have been fatal wounds, and even if they caused her no apparent pain, cumulatively they were enough to begin to impair her fighting ability. It was almost certain suicide, and they knew it, but if they were to die then they would do so making sure that this creature could no longer spread its evil through the world.
His two companions gave their lives while creating the perfect opening for Elrond to strike the killing blow. However, even as he cleft its neck in twain with his sword, the creature had its cold fingers sunk deep into the side of his own neck and was tearing away a wad of flesh as easily as a child might grab a handful of cake. His life's blood sprayed out across the battle-churned forest floor like that of so many before him. Elrond's vision was already fading to black as he hit the ground with the thing's headless body on top of him, its truncated neck oozing dark, rotten smelling blood into his mouth and open wounds. The last thing he heard was poor hamstrung Tareldir, now the sole survivor, frantically calling his name.
Death took him, but it did not keep him.
Elrond awoke the following sunset, feeling so very, very hungry. It was a hunger greater than he had ever known, greater than he had ever suspected could be possible, and yet it was accompanied by such a feeling of power that he would not trade it for anything. All his life, he had thought that elves had been created to be perfect, without any possible improvement over what they already were. Now he knew he had been wrong, because suddenly his body was so much stronger and his senses so much sharper than before.
For example, he did not need to follow the trail Tareldir had left while crawling through the underbrush, dragging his crippled legs behind him, because Elrond could still hear the elf, even though he had managed to cover nearly ten miles since the end of the battle. He could also hear every single animal between here and there, but Tareldir had been calling to him previously, and so Tareldir would have his answer. It was a matter of moments to catch up to him, and when he did, the elf's blood was so delightfully sweet that Elrond never even considered not drinking it all, because what else was it there for if not to sate his hunger, however temporarily?
When there was nothing left, Elrond stood, threw away the empty container, scented the air, and began running toward Imladris, glorying in such previously unattainable speeds. This was a gift which he needed to share with his children.