Infiltration of the British Ministry of Magic (1997)

The infiltration of the Ministry of Magic on September 2, 1997 by Harry Potter, Hermione Granger, and Ron Weasley was a skirmish of the Second Wizarding War. The three Dumbledore's Army members were able to sneak into the Ministry, which was under the control of Lord Voldemort, steal a Horcrux, and free multiple Muggle-borns who were imprisoned there.

Background
Salazar Slytherin's Locket was an heirloom of Voldemort’s maternal family and one of his Horcruxes. This was discovered at some point during the First Wizarding War by Regulus Black, a Death Eater who grew disillusioned with his side and turned against the Dark Lord. Regulus, with the assistance of his loyal house-elf Kreacher, tracked the locket to its hiding place in a cave in 1979. He replaced the locket with a fake one, leaving a note to Voldemort admitting what he did, and was killed by the Inferi in the cave’s lake.

Voldemort never learned of this, but Harry Potter, Hermione Granger and Ron Weasley deduced it in 1997. They questioned Kreacher as to what had happened to the locket, and he eventually told them what had transpired with Regulus and that Mundungus Fletcher had stolen the locket from Number 12 Grimmauld Place. Harry sent Kreacher to find Fletcher and bring him back to the Black household, where he and his friends were hiding out.

Fletcher admitted to taking the locket and told them that he was forced to give it up to a Ministry employee – Dolores Umbridge. The Ministry had fallen under Voldemort’s control in August, and Umbridge was the head of the new Muggle-Born Registration Commission, an instrument of discrimination against Muggle-borns. Harry, Ron and Hermione spent the next few weeks making a plan to sneak into the Ministry, the most “dangerous place in the whole world” for them to be at the moment.

Sneaking In
"Blooming pain in the bum, this, eh? Forcing us all to get to work this way! Who are they expecting to turn up, Harry Potter?"

- Ministry employee

The trio waited outside the Ministry under Harry’s Invisibility Cloak. Hermione stunned Ministry employee Mafalda Hopkirk, and then took Polyjuice Potion to take her form. The trio moved her unconscious form into an empty theatre nearby. Next, Reginald Cattermole arrived and Hermione gave him a “sweet” that immediately made him sick, and insisted that he go to St. Mungo's, despite his reluctance. Hermione and Ron then obtained hairs from Albert Runcorn to disguise Harry.

Once inside, Harry, Ron and Hermione split up to take GENTLEMEN and LADIES to get inside. Employees had to “flush” themselves in, though they did not get wet. They then found themselves in the Ministry Atrium, where the Fountain of Magical Brethren had been replaced by a statue of a wizard and witch seated on ornate thrones made from the bodies of Muggles “in their rightful place”. At the base of the statue read Magic is Might.

Splitting Up
"If my wife were accused of being a Mudblood – not that any woman I married would ever be mistaken for such filth – and the Head of Department of Magical Law Enforcement needed a job doing, I would make it my priority to do this job, Cattermole. Do you understand me?"

- Yaxley threatens Reg Cattermole (actually Ron Weasley)

They headed for the lifts, but were intercepted by Death Eater and head of the Department of Magical Law Enforcement Yaxley, who demanded that “Cattermole” fix his office, where it was raining. Hermione whispered advice on how Ron could fix the problem before the trio was forced to split up. However, Hermione was then pulled away as Umbridge arrived, believing that Travers sent her to record-keep. Harry was left alone with the puppet Minister for Magic Pius Thicknesse, and then went in search of Umbridge’s office.

As Harry searched for Umbridge’s office in hopes of finding Salazar Slytherin's Locket, he came across a pink pamphlet that read "Mudbloods and the Dangers They Pose to a Peaceful Pure-Blood Society". It was implied to have been written by Umbridge. Harry then found her office – with the magical eye of the late Alastor Moody on the door. Harry took the magical eye and searched the office, but could not find the locket. He did, however, find a file on Arthur Weasley that declared him to have “unacceptable pro-Muggle leanings” and to be under surveillance as a known member of the Order of the Phoenix and acquaintance of “Undesirable No. 1”.

Harry and Ron briefly met up again in the lift, where they ran into Arthur. He advised “Reg” on how to fix the rain in Yaxley’s office and then confronted “Runcorn” on turning Dirk Cresswell in as a Muggle-born who faked his family tree, forcing him to go on the run. Harry attempted to warn him about the Ministry watching him.

After Arthur got off the lift, Harry wandered about under his Invisibility Cloak trying to find Hermione, and his attention was caught when he noticed the presence of Dementors.

The Muggle-Born Registration Commission
Harry found a courtroom in which a wizard named Alderton was being tried as a Muggle-born. When he tried to protest that he was a half-blood, he was threatened with the Dementor's Kiss and then sentenced to Azkaban. Mary Cattermole was called next, and Harry entered the room to find that Dolores Umbridge was conducting trials with the assistance of Yaxley and Hermione disguised as Mafalda Hopkirk.

While Umbridge sadistically conducted the trial, she exposed the locket she was wearing around her neck. Hermione asked her about it, and Umbridge told her it was a Selwyn heirloom, a lie to bolster her “pure-blood credentials”. Harry, enraged, stunned her and Yaxley from beneath the Invisibility Cloak.

Umbridge’s Patronus vanished and the Dementor in the courtroom attacked Mrs. Cattermole. Harry used a Patronus Charm, while Hermione took the locket from Umbridge and left a copy in its place so that Umbridge would not later suspect the truth. She then freed Mrs. Cattermole from her restraints with a Revulsion Jinx. Harry and Hermione summoned their Patronuses and freed the other Muggle-born prisoners, telling them to flee the country while Voldemort remained in power.

Escape
Harry and Hermione met back up with Ron as they and the freed prisoners raced to the Atrium. Unfortunately, the Ministry’s security had been alerted, and there were workers sealing off the exits. Harry used his disguise as the intimidating Albert Runcorn to bully them into stopping momentarily. The Muggle-borns fled as the real Reginald Cattermole arrived and Yaxley appeared, ordering that the exits be sealed again.

Yaxley soon figured out what was happening and tried to stop them from escaping. He grabbed Hermione’s arm as she, Harry and Ron Disapparated. She used a Revulsion Jinx to force him to release her, but he was taken past the protections around Number 12 Grimmauld Place, forcing them to abandon it as a safe house.

Aftermath
Harry, Ron and Hermione obtained a Horcrux and retrieved Alastor Moody’s magical eye from the Ministry of Magic, and freed many innocent people who would have been prosecuted by the Muggle-Born Registration Commission. However, Number 12 Grimmauld Place was exposed to the Death Eaters, forcing the trio to move around in the wild for the next few months. Carrying Salazar Slytherin's locket with them also exposed them to negative energy that would eventually lead to Ron temporarily abandoning his friends.