Here's an idea, and snippet, that came to me a while ago. It isn't finished yet, I should note:
Godric's Hollow, October 31st, 1981
The Dark Lord Voldemort sneered in triumph as Lily Potter's lifeless corpse fell to the ground in the nursery. The thrice-damned Potters would defy him no more. He strode over to the cot that held the child. He looked at the small child that slept in there.
How strange, he thought to himself, that something so powerless as a toddler could have anything that could defeat him, the most powerful wizard of the 20th Century, more powerful than even the infamous Grindelwald. He drew his arm back, ready to cast the Killing Curse and end this threat to his reign. But then he paused, and lowered his arm. "No." he grinned to himself. "I have a better idea. Wormtail!" he shouted.
A few moments later a small sneaky looking little man appeared at the doorway. "You summoned me, my Lord?" Peter Pettigrew asked.
"Summon my Inner Circle, and the items needed for the Banishment Ritual." The Dark Lord declared. "The child is a threat to me, but I shall take steps to... neutralise it."
"At once, my Lord." Pettigrew said, and vanished. Voldemort looked again at the child and smiled.
"Who knows? Perhaps someone shall do my work for me, and then only those damned Longbottoms will be left...."
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If anyone had been able to peer into the windows of the Potter residence that night, what would they have seen? Six of the most feared Dark Wizards, and their master, marking the carpet of the nursery room with chalk, and placing a tiny child in the centre of a Magic Circle. Around the circle, the six Dark Wizards, amongst them Lucius Malfoy and the younger Bartemius Crouch. The Death Eaters, as the followers of Voldemort were known and feared by, began to chant the ritual. The room began to fill with magic, and Voldemort smirked to himself as the power grew and grew. Soon an image appeared in a sphere over the circle, showing a beach at night with the tide coming in. Voldermort drew his wand once more, and chanted the command words of the Ritual.
A jet of reddish-grey light burst from the tip of his wand, and hit the bassinet that held the young Harry Potter. There was a sound like silk being torn, and the bassinet rose up into the sphere and vanished.
Suddenly, Voldemort grabbed his wrist, as smoke began to rise from his trembling wand. His arm suddenly burst into golden flames, not unlike those of a phoenix, and raced over his body as he screamed in pain. The Death Eaters scattered as an enormous burst of magical energy exploded out from the Dark Lord, ripping the soul from his body and burning the corpse to ashes....
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Unaware of all this, the innocent child that was Harry Potter slept on, as his bassinet sped through the mists of time, past a police box, and a sports car, to arrive on that mysterious beach....
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Two men slowly walked along the beach front that night. One was barely an adult, still only 19 years old, while the other man was much older. Only two things connected the two men.
The older man suddenly raised his arm as he tilted his head. "Wait a moment. Frank, do you hear that?"
The young man, apparently named Frank listened as well. "Yes I can, Uncle Arthur..."
They approached the sound cautiously, and the older man knelt down. "Oh dear..." Sergeant Arthur Wilson said, as he picked up the child from the bassinet.
"Should I go get Mister Mainwaring, Uncle Arthur?" Frank Pike asked.
"I think you'd better Frank..." Wilson nodded. "I'll take him back to the guardhouse." he added, as Pike jogged off into the night. Picking up the child and the bassinet, Wilson carried them both away from the waters' edge.
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Well, there you have it. Harry Potter, as raised by Arthur Wilson from Dad's Army...