Disclaimer: J.K. Rowling owns Harry Potter. Is my name J.K. Rowling? I think that answers your question.

The night wet and windy, two children dressed as pumpkins waddling across the square, and the shop windows covered in paper spiders, all the tawdry Muggle trappings of a world in which they did not believe…And he was gliding along, that sense of purpose and power and rightness in him that he always knew on these occasions…Not anger…that was for weaker souls than he…but triumph, yes…He had waited for this, he had hoped for it…

"Nice costume, mister!"

He saw the small boy's smile falter as he ran near enough to see beneath the hood of the cloak, saw the fear cloud his painted face: Then the child turned and ran away…Beneath the robe he fingered the handle of his wand…One simple movement and the child would never reach his mother…but unnecessary, quite unnecessary…

And along a new and darker street he moved, and now his destination was in sight at last, the Fidelius Charm broken, though they did not know it yet…And he made less noise than the dead leaves slithering along the pavement as he drew level with the dark hedge, and stared over it…

They had not yet drawn the curtains; he saw them quite clearly in their little sitting room, the tall black-haired man in his glasses, making puffs of colored smoke erupt from his wand for the amusement of the small black-haired boy in his blue pajamas. The child was laughing and trying to catch the smoke, to grab it in his small fist…

A door opened and the mother entered, saying words he could not hear, her long dark-red hair falling over her face. Now the father scooped up the son and handed him to the mother. He stood and stretched, yawning…

The gate creaked a little as he pushed it open, but James Potter did not hear. His white hand pulled out the wand beneath his cloak and pointed it at the door, which burst open.

He was over the threshold as James came sprinting into the hall. It would be easy, too easy, he was not prepared

"Lily, take Harry and go! It's him! Go! Run! I'll hold him off!"

Hold him off!...He laughed before casting the curse…

"Avada Kedavra!"

Not meant to be very long. A prologue, like.

Do you know where this is from?

Kudos for you, if you do.