Umbridge is thrilled to see Mafalda and takes Hermione downstairs to take notes on the hearings. Harry gets out of the elevator, tells Thicknesse he's on this floor to speak with Mr. Weasley, and pulls out the Cloak as soon as he's alone. He begins to panic, thinking that they never made a plan in the event that they got split up. Harry decides to look for Umbridge's office on the off chance the locket is in it. He comes upon a room of young wizards and witches assembling pamphlets with information about the dangers of Mudbloods. Harry notices that Moody's eye is installed in Umbridge's office door so she can spy on the employees.
Harry recognizes that, while they spent lots of time planning a best-case scenario, they neglected to come up with a worst-case scenario plan—which means that now their planning is mostly useless, and they're going to have to go on skill, instinct, and the bits of information they do have. In other words, they now have to rely on a combination of knowledge and power, rather than focusing mostly on the things that they know.
Harry pulls out a Decoy Detonator, which scuttles away and starts emitting smoke across the room. He slips into Umbridge's office and pockets Moody's eye. He begins going through a filing cabinet and stops short when he finds Mr. Weasley's file, which reads that the family is being tracked in case "Undesirable No. 1" makes contact. Harry also notices Rita Skeeter's biography of Dumbledore on the desk and opens the book randomly to a photograph of young Dumbledore laughing arm in arm with a golden-haired young man. Thicknesse lets himself in and as he writes a note, Harry slips out.
Discovering Rita Skeeter's biography here reminds Harry of his doubts about Dumbledore, which (thanks to his focus on planning) he's likely been able to ignore for the last month. Bringing them back to the surface reminds Harry that he will still have to figure out how to come to terms with Dumbledore's legacy in a way that allows him to move forward and retain respect for his former mentor.
Deciding they need to leave and come back another day, Harry runs to the elevators. Ron gets in at the next floor and barely recognizes Harry, and on the next floor, Mr. Weasley and an old witch get in. He glares at Albert Runcorn with disgust and then addresses Reg, kindly suggesting a spell to use on Yaxley's raining office. Ron gets out and Percy steps in, only noticing that Mr. Weasley is there after the doors close. Percy gets out on the next floor, at which point Arthur angrily calls Runcorn out for putting Dirk Cresswell in Azkaban, but Harry cuts Mr. Weasley off and tells him he's being followed. Mr. Weasley gets out in the Atrium.
Here, Harry chooses to use the power afforded to him by Albert Runcorn to do something good and warn Mr. Weasley that the family is being followed—though this also puts Harry's disguise in question if Mr. Weasley chooses to question this further. This shows that doing the right thing could have all manner of consequences, good and bad, and that Harry is going to have to decide how to wield the power he's borrowing.
Harry puts on his Cloak and takes the elevator down to the courtrooms. As he tries to figure out if Runcorn has enough power to pull Mafalda out, he realizes that the hallway is filled with dementors guarding Muggle-borns. Knowing he can't conjure a Patronus without giving up his identity, he thinks of Ron and Hermione. A door opens and a screaming man emerges. At Umbridge's command, dementors take him away. Umbridge calls Mrs. Cattermole, and Harry slips into the room behind her. Umbridge, Yaxley, and Mafalda sit above a platform, while Umbridge's cat Patronus protects them from the despair coming from the surrounding dementors.
Seeing Umbridge like this shows Harry that, like Voldemort, Umbridge is only interested in power for power's sake—given what the reader and Harry know of Umbridge, these trials are a joke and aren't actually giving her any useful information; they're a way to intimidate people and feel powerful. With this, Harry is able to get an inside look at how a person like Umbridge can abuse power and align themselves with someone like Voldemort, even if they're not entirely a Death Eater.
Harry sneaks up behind Hermione and whispers to her that he's there as Umbridge asks Mrs. Cattermole who she took her wand from. As Umbridge leans forward, Harry sees the locket around her neck. She asks for a form from Hermione and Hermione compliments the locket. Umbridge says it's a Selwyn family heirloom. Harry Stuns Umbridge and Yaxley. He casts a Patronus to protect Mrs. Cattermole from the dementors as Hermione replicates the locket and takes the Horcrux. She conjures a Patronus to accompany them out and Harry tells Mrs. Cattermole to take her children and run. In the hallway, Harry tells the Muggle-borns that the new official position is that they should go into hiding and tells them to follow the Patronuses.
Now, Harry can use his power as Albert Runcorn to do even more good and hopefully, help these people get away and be safe. All the magic that Hermione and Harry perform here shows that all of what they learned at Hogwarts is now serving them very well in the real world. This suggests that, under good management and guidance—as the school was with Dumbledore—schools can prepare students to engage with revolutions and can give them the tools to think critically and fight evil.
At the elevators, Mrs. Cattermole throws herself at Reg/Ron. Ron tells Harry that the Ministry knows they're here. They and the Muggle-borns squeeze into two elevators and, at the Atrium, Harry uses Runcorn's power to command employees to stop sealing off Floo fireplaces. Harry threatens one man who contradicts him as the real Reg appears. When Yaxley approaches, Harry tries to bluster and deflect blame. Yaxley chases them out to the public toilet and Harry tries to Apparate with Ron and Hermione. It feels wrong, but they arrive at Grimmauld Place. Suddenly, Hermione Apparates with them again.
Just as when the trio escaped from the wedding, it takes all three of them performing important and different tasks in order to effectively escape from the Ministry. This impresses upon Harry once again that he couldn't do this alone; he needs Hermione and Ron in order to accomplish these tasks and will ultimately need to call on his wider community to truly emerge victorious.