Dumbledore manages to warp the mind of the backwards-aging Harry Potter against his own creation, and in a fight against Voldemort in a graveyard, the poor creature loses his powers and becomes a spirit. (After the fight, one of only two remaining faithful revives the poor Cedric Diggory, who goes on to be Turned by a sparklevamp.) Abandoned by almost all his disciples, who have lost faith in the mission, Voldemort goes looking for a way to regain his powers so he can continue to do good works, occasionally running into Dumbledore and Harry along the way.
Finally, in the end, Voldemort pays his master one last visit, when Harry has regressed to age one year old. He has regained enough of his powers where he intends to sacrifice his life to cure Harry's backwards aging. He tries, and fails to cure Harry, but miraculously regains his body and his powers. He immediately brings his master's dead parents back to life, as one last gift to Harry before moving on to find his disciples and carry on in Harry's name.
Crossposted from http://fayanora.dreamwidth.org