On his 16th birthday Harry gets rescued by Dumbledore from starvation only to sign some documents that will solve all problems. The soulution is a group marriage to Romilda Vane, Susanne Bones, Mariatta Edgecomb and Millicend Bullstrode. This group marriage heightens Harrys power as well as his spouses. Over the next year Dumbledore orchestrates their life so everyone thinks Harry has become Dark when he steals Voldemorts dead body and declares revenge.
As it turns out Dumbledore is in reality Nicholas Flamel who creates Dark wizards like Grindlewald, Voldemort and Harry so he can defeat them. The story is available as PDF.