Disclaimer: all credit for idea, plot, and general creativity to user E. C. R. Potter, and to JK Rowling, and Tolkien for writing the originals.
A sharp crack split the air as a twig snapped underfoot causing more than one of the masked figures to twitch violently in their robes. The air was heavy with an unnatural tension as the trees seemed press in from all sides.
"Why are we here?" Hissed one of the figures. He still gripped his wand tightly having instinctively drawn it at the sound.
"Because we are told to be, fool." Hissed back another, holding her wand just as tightly.
"Crucio." The curse was whispered almost lovingly as the man collapsed to the ground writhing, desperately trying not to scream his agony. A wraith-like figure walked from the shadows holding his curse for a long few seconds before letting it fall. "Do not question my orders Lucius, your failures have not been forgiven."
The pale creature smiled as Lucius grovelled in the dirt, begging his forgiveness, a smile that didn't reach his crimson eyes. He turned to his assembled deatheaters.
"Follow and walk where I walk - to stray from the path is death."
With that he turned and began walking, his dark greatrobe billowing despite the unnatural stillness. The deatheaters followed - fear of their master overwhelming any lingering fear of the forest.
Whether it was from a moment of pain-induced clarity or merely a flash of insight, Lucius recognised what was happening as they walked deeper into the stillness. It was repelling magic - designed to overcome the rational mind of any who would invade this place. If this amount of spellcraft was on the safe path, he was terrified to think what defenses could be found off it.
If indeed this they were actually on the safe path in the first place - try as he might he saw no sign of markers magical or mundane in the damp forest floor. Lucius forced himself to stop thinking about that he couldn't afford to even think such doubts - not when his very thoughts could be read like so many pages in a book by his Dark Lord.
Eventually they broke though the protections and sudden lightening of the atmosphere gave them greater speed, despite the sweat staining the black robes of many, and they soon broke out of the trees onto a rocky beach.
All but their master stopped short in a sudden fear as they beheld what lay before them - their eyes glued to the monstrous volcano that broke out of the sea like an accusing finger.
"But… How?..." One of the deatheaters began, abruptly cutting short when he realised that he was actually questioning his master. Luckily for him the Dark Lord merely smiled mockingly.
"The Black Sea was not always known by that name." Their master explained languorously, playing the benevolent emperor. "Before its lands sunk beneath the waves, this place was known as the Black Lands, and that is Orodruin." He gestured imperiously to the dark volcano and it's haze of smoke. "Mount Doom."
He paused to drink in the fear his words has invoked before raising his wand and casually conjured a ship in a casual display of frightening power.
As the ship drew near to the island one deatheater seemed to pull together the remaining scraps of his courage.
"My lord, um, may I ask what you will do in Mount Doom?" The deatheater's voice was shaky behind his mask.
His master turned slowly and favoured him with his second smile of the day. "I plan to gain more power than any mortal has ever dreamed of." His answer did nothing to reassure his deatheater.
"But… How will you defeat -" The Dark Lord spun towards him in sudden rage, blasting him backwards with a wordless curse.
"I am the most powerful Legilimens and Occlumens there has ever been!" His master spat. "Nothing can access my mind, nothing! Crucio." The curse lasted far longer than the one that had held Lucius earlier and when it was finally lifted its victim was wracked with dry heaves and left on the deck shaking uncontrollably.
None dared help him and when the reached the shore of Orodruin it was only the bone-deep certainty that if he didn't follow he would die that allowed to shaking deatheater to pull himself up and limp after the procession.
They were led unerringly upward following a path that was all but invisible unless you were already on it. That their master displayed a clear familiarity with the route that only further increased his follower's unease.
The path brought them to a forbidding entrance-way rough-hewn in the volcanic rock. Heat poured forth from inside. Their Lord strode inside not sparing a glance for the involuntary hesitation that hit each deatheater at the threshold.
As the Dark Lord's faithful followers entered, dusting the air with cooling charms as they did, they found themselves on a jutting outcrop. They could not help but look down in trepidation at the roiling magma that burned hundreds of feet below them.
Words that were somehow painful to hear began to echo from in front of the deatheaters and some even glanced around in fear before realising that the twisted speech was coming from their master. Not all of the sounds seemed humanly possible and each of the rough syllables seemed to somehow evoke great pain.
And yet somehow the watchers could understand every word.
"One ring to rule them all, one ring to find them, one ring to bring them all, and in the darkness bind them."
The echoes of the words did not fade as they should and while the twisted mutterings still stained the air their lord gestured complex magics with his wand. As he did so the sounds grew louder as if several voices beyond comprehension whispered eagerly from the walls.
Something arose from below - a small point of light glowing with heat. Their lord gestured one final time with his wand and held out his hand. The point twisted and lengthened before shaping itself into the form of a ring.
"Sauron." As their master spoke his final word of the ritual it gathered with the echoes of the room and as the ring slipped onto his finger the whole room seemed to echo back a single word before falling silent.
"...Voldemort..."
Hundreds of miles away an ageing man started awake in his favourite chair and glanced around at his study. He could feel something was deeply wrong. Many decades of his work had so attuned him to the magic of our earth that he could feel the tremors caused by the joining of two such beings of power.
The man tried to rise but collapsed back - his shaking knees unable to support him. This changed everything.
His eyes filled with tears as he looked at the walls of his school and silently counted the lives that would surely be lost.
"Oh Tom... what have you done?"