At the end of every road (слэш)

One would think traveling 52 years into the past would allow Harry some much desired anonymity, but unfortunately the malfunctioning Triwizard Cup spat Harry out on the quidditch pitch in the middle of a game. There's no lying about his provenance while a shiny plaque on the base of the Cup announces to everyone he is 'Harry Potter, Hogwarts Champion, 1994.'
Swept up by the ministry and sworn to secrecy by the Unspeakables, Harry is left to navigate the past on his own. Good thing his great-grandparents are willing to take him in - even if they're a little more into blood purity than Harry had expected - and Hogwarts is willing to welcome him back - even if he's a novelty to everyone as the time traveling Champion.
At least Harry will have the familiarity of Gryffindor Tower to ease his homesickness. Or he would, if the sorting hat hadn't put him in Slytherin, where he's forced to share a dorm with none other than Tom Riddle.
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In which Harry is determined to prevent Voldemort's rise, even if he has to stalk, bribe, threaten, and marry Tom Riddle to do it.