Edit: I know that this first chapter is rough with little detail and a few issues with flow. Please dont give up here and take a few minutes to read chapter two. If you still dont like it then please leave me a comment so that I may improve my future work.
Disclaimer: I don't own any of this material other than the method I used to twist the world created by others better than myself.
(For my purposes Flint is only a year older than Harry)
Marcus watched as the Death Eater grabbed his mother by the scruff of her neck and pulled her up to meet his gaze. "You think what I did to your husband was bad?" He said maniacally, he leaned in to her ear and Marcus could only faintly hear him whisper, "Wait till you see what happens to you!" He drew his wand and uttered a curse that Marcus had never heard before and never heard anybody else utter from that point on, he could only faintly hear the words, but to him they were clear as day, and he never forgot them from that moment for the rest of his life.
Marcus could only watch as the Death Eater pulled his mother's soul right out of her forehead. Slowly it came, like that string of cheese that refuses to let go of the rest of the pizza. But it wasn't the sight that burned that memory into Marcus' mind. It was the sound. The sound of his mother's death screams. Only she wasn't dying, at least not physically.
The sound of his mother screaming seemed to last an eternity.
When the curse had finally run its course the Death Eater dropped Marcus' mother next to his father's body like a sack of gravel.
The Death Eater then turned to Marcus with a smile on his face and stared at the eleven year old boy who had just watched his parents die before his very eyes. He was wondering how things could go from happy joyful news, to death and destruction so quickly. The Death Eater noticed the piece of paper that the boy still clutched in his hand, Marcus grasped the one happy thing in the room even tighter.
The Death Eater crossed the distance of the tiny room in three strides and had Marcus held up by the collar of his shirt and walked him over to show the boy his handiwork up close, "You see what I did to them? I could teach you many more powerful spells and magics if you joined me and the Death Eaters." Marcus gave the Death Eater a swift kick to the only place his short legs could reach. The Death Eater howled in pain as he dropped Marcus next to his mother and father. For a long moment Marcus stared into his father's eyes trying to make himself believe he was dreaming. But when the eyes just stared back at him, unblinking, unloving, Marcus turned to his mother for comfort. She blinked very slowly. Not a blink of one waking from a stupor as Marcus had hoped for, but the blink of one whose eyes were drying out and need to be moisturized. The blink of lifelessness.
It was that moment when Marcus snapped out of his stupor and resolved himself to fighting to the bitter end. He reached over slowly while the Death Eater was still distracted by his pain and grabbed his father's wand. His father had never taught him how to use it. But had assured Marcus that if the time ever arose when he needed to use it, he would be able. Marcus tucked the wand in his sleeve as he heard the Death Eater glide over to him.
As the Death Eater raised Marcus by his collar for the second time, Marcus did not show his fear, though his mind was racing to find a way out of this and was drawing blanks at every turn,
"So, you are too good to join our ranks? No matter, I shall kill you slowly, make you bleed, make you beg for my mercy before I am done!"
As the Death Eater raised his hand the only thought that managed to wriggle its way into Marcus' head was of the fun that him and his father had making their own fireworks by throwing explosives in the air and blowing them up with spells. As the Death Eater began his spell Marcus quickly raised the wand and screamed at the top of his lungs, "BOMBARDA MAXIMA!"
As Marcus was blown back into the wall his last sight, before fainting, was of his letter from Hogwarts burning as embers from the fireplace, blown around by the spell, set the house ablaze.