Lord Voldemort has won, and he has won at a terrible and bloody price. He conquered Magical Britain, and then his agents in the rest of the magical world brought down their governments so he could conquer them as well, practically overnight.
Harry Potter failed, and then he ran along with everyone who was left. They had one last chance, one last gambit. They would send Harry through time to long before Voldemort rose to power, and it would be Harry's task to discover the secrets of his immortality and kill him. But the path of righteousness had already failed them, so Harry resolved to walk a darker road.
Severus Snape shivered. The meeting place that Lucius had given him was in the middle of an Irish forest, and it was freezing. He shivered again, but not from the cold. He was trembling with… something, a kind of anticipation. It wasn't excitement, he knew that, but his whole body seemed to vibrate, it was as if his flesh could sense the importance of this night, the weight of the change that was about to consume him. . He heard a faint murmur ahead and paused. Pulling the blank white mask from his robe and fastening it over his face, Severus stepped out into a clearing filled with hooded and masked figures. Most wore blank masks like him, but there were a few, hanging around the edges, eyes trained on the trees and stances ready for anything, that wore the silver skulls of the true death eaters, the marked followers of the Dark Lord. One approached him as he walked to join the others, and he recognized Lucius' eyes gleaming out from the orbit's of the deathly mask. . "Severus, I am glad you could make it." Lucius' sibilant whisper sent a shiver down his spine, the greeting was almost proud. . "I would not miss it for anything." . It was true, all the things that may have held him back were gone. His thoughts flashed briefly to Lily's face, and his expression soured to a grimace under his mask. (edited)
Lucius did not see the change, and he turned away in satisfaction. . "Go and join the others, the Dark Lord shall be here soon." . Severus strode quickly over to the others and took his place in the center of the crowd. He didn't speak to them and they didn't offer any greetings either. The silence was tense, expectant, and soon to be rewarded. . A chill filled the air and a great inhalation came from somewhere to Severus' left, and he slowly turned his head to see what was there, even though he already knew. . Two pairs of eyes shone in the darkness, one a bloody red, the other a plague-like green. The men walked slowly into the clearing, the red eyed man came first, clearly the superior of the two. He was tall, with fair skin and rich, dark hair. He wore fine robes of black silk, and when he gestured widely to them in greeting, Severus could see the red satin that lined the inside. His smile was warm, but his eyes burned. The other man came slightly behind him, not in subservience, but respect. He wore a strange garb made of a thick, stiff looking fabric colored a dark grey, so dark it was almost black. He wore a sash around his waist, and it was gathered into a large metal ring where a belt-buckle would be, before flowing down in front of him. His coat was almost like a muggle coat, but there was a short cape around his shoulders. He wore an iron mask over his face, a twisted, featureless thing, only the man's eyes were visible. They were cold, as cold as the Dark Lord's were fiery, and they pierced the souls of every person in the clearing.
The Dark Lord and his apprentice, the two most powerful dark wizards to walk the earth. They said that Voldemort was immortal, that his spirit had transcended the limits of the body, and that he would rise again in a new and more terrible form if any should slay him, and that he would do this again and again, forever. His apprentice, the faceless man, was similarly mythologized. People said that he was invincible, that he had delved into ancient rites and forgotten rituals, that he had uncovered secrets that none had ever known. They said he had damned himself, and that in exchange for his damnation he had received great power. A master of sacrifice, some said, others called him a lord of pain. . The stories had seemed too good to be true, myths and legends, but as Severus stood there, the eyes of the two men judging him and his comrades, he found himself believing them.
Harry goes back in time and, instead of fighting Voldemort, joins him. He does this in the hope of learning Tom's secrets and finding a way to defeat him, but more than that, of finding a way to destroy his empire from within. Inspired by the Sith "Rule of Two", Harry will become a Dark Lord in order to kill one, but of course Voldemort will not suffer rivals, and so it is only a matter of time before the war for magical Britain becomes a three-sided affair.