Septimus S Snape

"you have the chance to change the future if you accept me." was what the ghost said, the potion's master stared at it for moments. "you're telling that potter and me sent our future's ghosts to the past!" Was the irrational reply. Time travel fic including Severus and harry, lordship, Pre-Hogwarts schooling, severitus by blood adoption. Genius!Harry. Canon until last battle.