Harry Potter and the Witch Queen

Harry Potter never actually beat Voldemort, but rather fought him to a standstill while Europe burned around them. Finding himself an unwilling part of a dark ritual to send him back in time twenty years, he is surprised to see how Dumbledore reacts to proof of obvious child abuse (Harry's), how eleven-year-old super genius and Witch Queen in training Hermione reacts to actually having a socially competent friend (Harry), and how much easier it is to shrug off the insults of munchkins when you're a grizzled war veteran.
But there is one huge problem: being sent back blew out his magic entirely. Just waving his wand knocked him out the first time he tried it. Can Hermione help him though his classes even with his magic almost unusable? Will Harry be able to find the secrets to actually killing the Dark Lord and saving his friends from a horrible future without blowing his cover, or even getting mistaken for the Dark Lord himself? Will Neville Longbottom get better grades than him?