Harry is sure that Kreacher's mission will only take a few hours, but the elf isn't back by night. Ron notices two cloaked men waiting outside, and Hermione reasons that, if they knew that Harry was here, they'd have sent Snape in. She thinks that Snape has probably been here, but Moody's curse kept him from telling others how to get in. Hermione and Ron start bickering, so Harry excuses himself. In the hallway, someone lets himself in and Harry points his wand at the intruder. Hermione and Ron join him as Mrs. Black's portrait screams. Lupin announces himself and praises Harry for testing his identity. They head to the kitchen.
At this point, Lupin exists somewhere between friend and mentor for the trio. While they're all adults now and while Lupin has no power over the trio, per se, in times like these, he can still step into the role of teacher and help them figure out how they should respond when a strange person enters Grimmauld Place. The fact that their relationship exists in this liminal space, however, continues to show that Harry and his friends haven't yet come of age completely.
Lupin is aghast to hear what happened on Tottenham Court Road. He doesn't think Harry has the Trace on him and explains that most of the wedding guests Disapparated before Death Eaters arrived. They seemed to not know that Harry was there, and Lupin says that Scrimgeour apparently died refusing to give away Harry's whereabouts. The Death Eaters searched every home connected to the Order and interrogated everyone—they now have the power to do whatever they want. He pushes a copy of the Daily Prophet at Harry. The headline reads that they want Harry for Dumbledore's murder. Lupin says that the coup was so quiet that nobody knows the truth, and blaming Harry makes people afraid that the resistance isn't legitimate.
By creating this environment of fear and suspicion, Voldemort has effectively made it so that nobody who would resist him feels like they can safely do so, given that it seems as though even Harry isn't a trustworthy person. By fracturing the community, Voldemort also makes it harder for Harry to ask anyone for help, given that many people will likely suspect that the Prophet is correct and that Harry isn't on their side. With this, Voldemort preys on people's grief and loyalty to Dumbledore and turns Dumbledore's death into something that serves him.
Lupin says that the Ministry has also started to "survey" Muggle-borns and are rounding them up and accusing them of stealing magic. He explains that attendance at Hogwarts is now required, and all students must prove that they're descended from wizards before being allowed to attend. Lupin confirms that Harry is on a mission from Dumbledore, offers to accompany the trio, and insists he doesn't need to know what the mission is. Hermione asks about Tonks and Lupin says she's pregnant as though he's admitting something nasty. He says that Tonks will be safe with her parents.
By requiring attendance at Hogwarts, putting these conditions on who can attend, and dictating the kind of education that students will receive, Voldemort now has control over how students will grow up and learn to think about the culture in which they live. By doing this, it will be far easier for Voldemort to poison students' minds and bring them over to his side, as they have no choice but to attend or face imprisonment.
Lupin insists that James would've wanted him to protect Harry, but Harry says that James would've wanted Lupin to stay with his baby. Harry and Lupin fight and Harry suggests that Lupin is abandoning his family and behaving like a coward. Lupin insists that he shouldn't have married Tonks and shouldn't have risked passing on his werewolfism to a child before cursing Harry and leaving. Both Ron and Hermione reprimand Harry, but Harry asks if it'll be worth it if Lupin goes back to Tonks.
In this moment, Harry steps into an adult role to chastise Lupin. Harry's reaction is certainly rooted in the fact that Harry grew up without parents and believes that children should have their parents if possible, especially when the few father-like mentors that Harry had were with him for such a short time.
Harry starts to flip through the Prophet that Lupin brought until he finds a photo of Dumbledore's family and an excerpt from Rita Skeeter's book. It talks about how Kendra moved the family to Godric's Hollow after Percival went to Azkaban and hid Ariana there. Many believe that Ariana was a Squib and that Kendra was ashamed of her. Harry feels horrible and wants to figure out how to confirm this.
That Kendra was possibly ashamed of Ariana being a Squib reminds the reader that the kind of intolerance that Voldemort promotes isn't something new; if this story is true, Voldemort is just a horrendous and extreme incarnation of something that's been plaguing the Wizarding world for decades.
Kreacher Apparates into the kitchen with a crack, bearing Mundungus. Hermione takes Mundungus's wand and Ron tackles the struggling man. Mundungus gives excuses for why he Disapparated during Harry's move, but Harry starts to ask about the locket. Kreacher hits Mundungus over the head with a saucepan, but Harry calls him off. Mundungus explains that he had to turn over the locket to a toad-like "Ministry hag" with a bow on her head when he was caught selling without a license. Harry realizes that the "hag" is Dolores Umbridge.
Hitting Mundungus with the pan shows that Kreacher's loyalties have truly shifted since Harry showed Kreacher respect and kindness. With this, Harry is reminded that all of his actions have major consequences. Just as Sirius's thoughtless indifference to Kreacher cost him his life, Harry's respect for Kreacher now might have even more meaningful results.