On Halloween 1981, Voldemort wakes up as a horcrux in Harry's body. Desperate, he decides to merge his own soul piece with the toddler's. His actions involuntarily land him on the other side of the prophecy... in the role of Harry Potter.
Young Albus Dumbledore, in desperate need of a proper friend, devises a spell to bring powerful wizards to him—only, he just might have been a tad overzealous. Result: the temporal displacement of Harry Potter and Tom Riddle to the year 1912.