Disclaimer: I don't own a thing. Pretty much it.
Note: At this point Marcus has been held back a year to be in line with Potter (Ill explain later)
Of all of Markus' memories, the last few he had consisted of his parents death and other various terrible thoughts.
He was so terrified by these last few memories that he couldn't process the fact that he was knelt down face to maw with a Dementor, its black hood rippling in the non-existent breeze. Or was it the breeze from Markus' soul slipping from his mouth to that thing's maw?
As Markus' higher reasoning slipped away, he pondered his current predicament. How had he come to be here? He struggled to recall even memories that he considered bad, not horrible but bad. The Dementor took them like a bitter sweet desert.
He fought to remember. He had had an argument with his girlfriend, what was her name? He couldn't recall as more of himself was slowly devoured by that thing in front of him.
Marcus could only recall the bad things. The argument about something "important", and storming away in a furry, as he was prone to doing. He went for his customary walk in the woods to clear his mind. He should have taken a hint from all of the patrolling teachers that something was wrong.
Marcus was forced back to reality when even that was taken from him.
Marcus struggled with all his might to think of a way out of this, but his mental capacity for creative thinking was gone.
Then came the one memory he knew the Dementor would leave with him for eternity. That horrible night five years ago when his parents... well you know the rest. But the Dementor had altered this memory to be even worse. No happy letter from Hogwarts to clutch in his small hand. Only the man towering over him. His father's last stand. His mother's last screams. All of it in high definition.
Then it came to him. The darkest (and last) memory he possessed held the key to his salvation.
Marcus tightened his grip on his father's beaten and battered wand. He placed the wand against the back of his own head and pointing through his own skull at the beast still savoring his juicy meal.
With the last strength he possessed Marcus uttered the curse that had had been stuck in that memory in the back of his head for five years.
Marcus felt more than saw the Dementor's surprise that its meal was fighting back.
Marcus regained his memory of his fight withe Melody, that was her name!
He used what little he had of her, her smile her laugh ,her flowing hair, all of her good qualities he used to fight the beast and with every detail the Dementor lost ground, and Marcus took it in spades.
He laughed out loud, a short burst but it unsettled the beast towering over him.
With parts of his soul in its rightful place he have one good tug on the invisible rope they were fighting over. Finally the Dementor gave and the whole strand they were fighting for slammed into Marcus' forehead as he was knocked to the ground by the force.
He glanced at the defeated Dementor as it burst into a fine dust that dissipated quickly. He sighed with relief.
He then noticed movement in the trees. Three more Dementors glided slowly toward him, taking their time as they knew Marcus was too weak to do the same to three of them at once.
Marcus swore out loud.
As he struggled to get up and failed miserably, he heard a voice in the distance shout "EXPECTO PATRONUM". Marcus' last sight before he lost consciousness was of a great silver stag galloping across a frozen lake.