DON’T READ THIS if you don’t want to know what might happen in the next Harry Potter book. But basically, here’s my thinking: Lord Voldemort, we know, stashed pieces of his soul in places like an enchanted diary and a ring, so he couldn’t easily be killed. We also know that Harry Potter’s scar links him metaphysically to Voldemort. As people have speculated, what if the scar was a Voldemort horcrux? That might explain why Voldemort’s killing curse didn’t work on Harry, but rebounded to send the Dark Lord to near-oblivion. And why Harry has his psychic link, his scar hurting when Voldemort is near or having powerful emotions. Now it’s clear that Voldemort did not give Harry a horcrux on purpose. At the end of Harry Potter and the Goblet of Fire Lord V clearly says he tried to kill Harry and doesn’t know why he failed. Dumbledore (whose name sounds too much like mumbo-jumbo) says it was an ancient and powerful magic — a mother’s love — that saved Harry, when Lily sacrified her life trying to save him. But that’s too pat — and already revealed. So the key mystery left, if Harry’s scar is a horcrux, is figuring who put it there and how. One theory is that Lord V somehow broke an unbreakable promise by killing her. Maybe, but doesn’t explain enough. We do know that a death has to occur to create a horcrux. Possibilities:
Voldemort planned to kill Harry and put a Horcrux in Lily. When she sacrificed herself, it reversed the spell, putting the horcrux in Harry.
Lord V had created a horcrux after killing Harry’s dad, and Lily altered where it was created, by sacrificing herself. Or perhaps she somehow put this object on Harry’s forehead, where it absorbed the curse and save him, as it left a mark or even part of Voldemort’s soul.
Lily created a horcrux switch. Could she have used her death to put a piece of Harry or herself in Voldemort, which somehow ruined his whole soul-saving setup? (If hers, could she come back?) If a bit of Harry’s in Lord V, this would really explain the prediction that one must die in order for the other to live. Harry has to get the rest of himself back by killing Voldemort, and vice versa. Kinda of like this twist, although it still seems rough around the edges.
Finally, Snape did one of the above. This I like even more. He loved Lily, fans think, and he’s portrayed as a villain, always picking on Harry, acting nasty as can be. But he keeps proving he’s on Dumbledore and Harry’s side, suggesting it was all an act, and he’ll be revealed as the ultimate hero, who not only saved Harry’s life by doing some cool trick with horcruxes, but is the magical master who should have been teacher of the dark arts all along.