June 1995: Percy Weasley leaves the Burrow following a heated row with his father, taking all of his belongings and renting a small flat in London. Unfortunately, since Diagon Alley is prohibitively expensive, he has to settle for a flat in Muggle London. Already somewhat inclined to dislike Muggles because of his father’s obsession with them, he finds them to be, almost without fail, rude, brutish, and overall very nearly uncivilized.
August 1995: Percy acts as scribe for Harry Potter’s trial before the Wizengamot. He refuses to acknowledge him, and thoroughly believes he is as unbalanced as the Minister claims.
September 1995: Ron becomes Gryffindor prefect. Percy writes to him, congratulating him for becoming prefect, and warns him away from Harry.
December 1995: Molly sends Percy his Christmas present. He doesn’t want anything to do with them, so he sends it back.
September 1995 - May 1996: Percy thoroughly approves of Minister Fudge’s and Dolores Umbridge’s plans to make Hogwarts safer for its students. He believes that it truly is best for them to know defensive magic theory, and theory only, because the Ministry will protect them. As he continues to live among Muggles, he grows to find them more and more distasteful, and also grows more resentful of his father and his infatuation with them.
May 1996: It becomes apparent that Lord Voldemort is, in fact, alive and returning to power. Percy is concerned for what this might mean for the Ministry. He knows he’ll stay faithful no matter what, but others might become scared; might leave the Ministry because of the threat. He can’t help but voice these concerns, and the only person who takes him seriously, or listens at all, is Yaxley, in the Department of Magical Law Enforcement. He takes Percy under his wing, tells him that the only way to make sure the Ministry remains strong is to weed out the weakest links - people who don’t have the wizarding world’s best interests at heart. Though he’s vague at first, it grows more and more clear that he means Muggleborns and those who love Muggles - they have split loyalties, and can never care for the wizarding world, and the Ministry, the way a pureblooded wizard can.
October 1996: Percy receives a letter from Dumbledore asking him to spy on the Ministry for the Order of the Phoenix. Percy writes back and says no. He disapproves of Dumbledore’s tactics, attempting to manipulate him by using his sister’s safety as a pawn, and this firms his decision to stand with the Ministry, no matter what.
December 1996: Percy visits his family with Minister Scrimgeour for Christmas, and is summarily chased out by the twins and Ginny. It is at this time that he realizes his family hates him, and he hardens his heart towards them in return. He was only trying to keep them safe, and this is how they repay him. That night, he practices saying, “I hate you, Father,” to see if it hurts.
It feels good.
June 1997: Albus Dumbledore is killed. Though Percy privately thinks the old man had to know it was coming, hanging out with such a dangerous crowd, he doesn’t say anything aloud, and attends Dumbledore’s funeral with the Ministry representatives.
July 1997: Yaxley returns from Azkaban, and a devastated Percy demands to know why he was captured and taken prisoner if he was only doing what’s best for the wizarding world - why he infiltrated Hogwarts and tried to kill Dumbledore. Yaxley explains that he had no part in trying to kill Dumbledore, and that they were merely trying to replace him as Headmaster, and it did get forceful, since Dumbledore refused to listen to reason. He couldn’t give his all to the wizarding world, Yaxley explains. He loved Muggles too much. Hogwarts needs someone who has the wizarding world’s best interests at heart, who will put pure-blooded wizards first.
August 1997: Bill Weasley and Fleur Delacour are married. Death Eaters attack the wedding. Amongst others, the bride and groom are killed, and several known members of the Order of the Phoenix are captured. Harry Potter, Ron Weasley, and Hermione Granger escape. Minister Scrimgeour is killed as well, Pius Thicknesse is his successor, and Yaxley is bumped up to head of the Department of Magical Law Enforcement. Percy is called down, and it’s revealed that he needs to prove his loyalty to the Ministry, though he’s assured it’s no more than what they’re asking of the rest of the employees. His assignment is to interrogate a known member of the Order to find out where Potter went, to protect him - of course.
The known member is Arthur Weasley.
At first, the interrogation is almost civil: Percy tries to think of as many ways to ask his father to reveal Potter’s location as he can, but Arthur insists that he doesn’t know, he doesn’t know, and Percy is sure he’s lying. After two days of this, Percy snaps, and ends up using the Cruciatus Curse on his own father. It only takes two repetitions of the curse before Arthur’s heart gives out.
Though Percy is horrified by his own actions, Yaxley reminds him that it was for the best; that Arthur didn’t have the wizarding world’s or Potter’s best interests at heart - that, likely, his love for Muggles made him blind to that. His death is tragic, of course, but no one holds Percy responsible.
September 1997: Harry Potter, Ron Weasley, and Hermione Granger infiltrate the Ministry to attempt to get information. They come across Percy in the lift, and Ron forgets himself and attacks Percy, even going so far as to attempt an abortive Killing Curse. Horrified at what he sees as a deliberate betrayal, Percy immobilizes Ron and Stuns the other two, turning them in to the Department of Law Enforcement. Hermione and Ron are killed immediately and their bodies are burned, and the Dark Lord is summoned to kill Harry personally. Harry is murdered, and his body is hung in a gibbet cage in Diagon Alley as a warning.
Unable to pretend any longer, Percy realizes that his family does hate him, and there’s no going back. He swears loyalty to Lord Voldemort and is Marked.
December 1997: The few shops in Diagon Alley that have yet to swear loyalty to Voldemort are razed. One of these stores is Weasley’s Wizard Wheezes, and the two owners are trapped inside. Their bodies are never found.
January 1998: A small splinter group of rebels makes their intentions to keep up the fight against Lord Voldemort clear. Though their identities are closely guarded, it’s suspected that some of the members include Luna Lovegood, Neville Longbottom, and Ginny Weasley.
April 1998: Pius Thicknesse is removed from the position of Minister for Magic, since the Imperius Curse is affecting his brain, and killed, and Lucius Malfoy is his successor. Percy is named his personal assistant, and they work together to form a better world for pure-blooded wizards.