A Muggle collaborates with a Wizard to take over the world. Unlike Voldemort, they try to subtly take over things, changing laws gradually, rearranging how the schooling system works, slowly phasing out the old guard at the ministry by hiring wizards willing to break the secret, etc....
The "heroes" won't stop them. The process will be so gradual, that by the time Harry is 70, he will be wondering why everything changed, but it's too late to do anything now. After all, he lived a comfy life, right?
