Dumbledore had also hired Remus Lupin to be the instructor for the Dark Arts course since once again the school had lost their teacher in that subject before the former year was over. At least, Harry hadn't killed Lockhart. Indeed, he hadn't done anything at all to the fraud. Nor was it in any manner his fault the Fraud had been dragged into the end of the year conflict. Ron had selected him as the go-to teacher. Not Harry. Harry wouldn't have chosen such a useless fop to drag along if he'd had his choice in the matter. Of course, given Harry's feelings about the teaching population at the school and the fact he hadn't even wished to take part in the fiasco, Harry wouldn't actually have taken any of the staff down there with him and Ronald knew it. But Dumbledore had wanted the Fraud to be part of the end of the year event so Ron had made sure to grab him before getting Harry from his room. Harry could only wonder if this teacher would last the year and if not how would his contract be brought to an end.
Remus was a good teacher who taught at both a pace and a level his students could understand and enjoy while still learning. What Harry hadn't known until almost the end of the year was the connection between his father, Remus Lupin and the escaped convict who was supposedly out to finish the job he had begun twelve years earlier on the night Lord Voldemort had attacked the Potter family.
Of course, the only reason he found out was because Sirius Black got impatient and attacked Ron on their way back to the Castle from Hagrid's cabin where they had gone at Hermione's insistence, to comfort Hagrid due to the upcoming execution of his semi-pet, Buckbeak. Hagrid had picked up Scabbers, Ron's rat, earlier that day when he had found it scavenging in the Forest and brought it back to his cabin. He'd checked the rat over and fed it but wanted to keep it under observation for a day since it wasn't looking too good to Hagrid's animal loving gaze before sending a message to Ron telling him he had something that belonged to him.
As they were walking back to the castle, Sirius, in his Grim form, had attacked Ron trying to pry the rat out of Ron's grip. Ron refused to let it go so Sirius had dragged the bellowing boy by a pant leg and his robes into the shelter of the Whomping Willow so he could transform and try to convince Ron to give him the rat. Harry, who still hadn't managed to convince himself Ronald really wasn't his friend, and Hermione had chased after the pair. Both of them were determined to stop any harm from befalling Ron. Once again, Harry had gotten drawn into risking his own neck over an endangered student. Upon seeing Sirius facing Ron in that room, Harry had given Hermione a scathing look which she either didn't see or chose to ignore because she was focused on Ron. But he knew the only reason he had to deal with this was because she'd insisted on comforting Hagrid in his hour of need and dragging Harry and Ron alone for the ride.
Remus Lupin claimed he had heard the ruckus and came running in a few seconds after Sirius regained his human form so he could talk to the three teens. The day after the event, while he was supposed to be on lockdown in the infirmary, Harry had been spying on Dumbledore's office via the use of his special cloak. He discovered Dumbledore called Remus up there for a full report on what had occurred. Harry knew it was mainly to see if there was anything he could hold against Harry in the future though there was a possibility that Remus was unaware of that. Remus had used the Marauders Map to see Sirius and Peter were with Harry, Ron and Hermione and that was why he had shown up when he did. Hearing that, Harry had snuck down to his rooms and stolen back his map because there was no way he'd let that fall into the Headmaster's hands.
But when Lupin had shown up in the quarters under the Willow, Harry hadn't known any of that. Chaos had ensued until Harry, who's head was spinning from the volume of noise he wasn't at all used to any more, bellowed for quiet. Then one by one he had Sirius, Ron and Remus tell their stories. Hermione, for once, had remained quiet just observing as Harry listened to each of the others.
In the end, all four of the other people in the room were looking to Harry for a decision as to how things would play out. Would he believe Ron that Scabbers was really just a normal rat? Would he believe Sirius that Scabbers was the true betrayer of the Potter family that Halloween night? Or would he believe Remus that Sirius had betrayed James, Lily and Harry himself before chasing after Peter and killing him as well? And was now taking the opportunity to try and add Harry to his kill list.
Harry decided there was a sure fire way to prove who was telling the truth and that was by letting Remus and Sirius try to break any animagus spell they claimed was on the rat if it really was Peter. If it broke, then Sirius was telling the truth provided the person the rat became turned out to be the long thought deceased Peter Pettigrew. If it didn't break though. Then it seemed Sirius had a problem with rats and Remus would take him out to meet a Ministry official for the carrying out of his sentence. Naturally, Ronald was angry that Harry hadn't just automatically taken his side because in his eyes this proved Harry wasn't as loyal to Ron as Ron pretended to be to Harry.
They had just found Sirius was telling the truth when Professor Snape, the teacher who hated everything Potter, (which was how Harry knew for certain the man not only could but would hold a grudge for every wrong done him whether real or imagined), came barging into the room sneering, snarling and foaming at the mouth about how he had them dead to rights this time and this time he'd see to it they all paid. Dumbledore wouldn't be able to make excuses for them this time and he'd finally succeed in getting Harry bloody Potter expelled for all his sins. There would be no more children harassed and bullied or hurt by a Potter in Hogwarts. In addition, he'd see justice served against Sirius Black. And Lupin as well since it was clear Lupin had been in touch with the fugitive. Sirius Black would die by dementors kiss before the night was out if he had any say in things and since he had them at wand point clearly he did have a say in things.