Hermione ran back to the castle after leading Madame Umbridge out to the centaurs. She was hoping that they put the fear of God or Merlin into her. She was such a horrible woman after all, causing all that pain and hardship. And poor Harry's hand. Hermione wanted to ask Professor McGonagall what she knew of the blood quill. After all, Harry was ready to go haring off after Sirius, and no one was sure what was going on.
When she returned to the castle, Harry was talking to Kreacher on the floo. Hermione happened to see his face when he told Harry that Sirius was gone.
"Harry, he's lying. Look at him!" Hermione exclaimed.
"Are you?" Harry demanded. "Are you lying?"
"Like Kreacher would tell the truth to the half-blood. Or would he?" Kreacher cackled to himself. At this Sirius was roused from his drinking to find out what the noise was.
"Harry, what is going on?" Sirius was worried.
"Oh, you are OK. That is wonderful. Voldemort gave me a fake vision. I thought it was real, like the one of Mr. Weasley." Harry was relieved.
They settled that Harry would stay in the school and Sirius would contact Dumbledore.
Harry, Hermione, Ron, Ginny, Neville and Luna were all talking in the Gryffindor Common room. No one was sure how Luna managed to be there, but they chalked it up to her being Luna.
Professor McGonagall walked in to speak to them. "Well done, children. Dumbledore was able to prevent Voldemort from gaining access to what he was looking for, and no one was injured. I'm glad you did not go off on your own!"
"Professor, did you know that Madame Umbridge was using a blood quill for her detentions?" Hermione demanded from her head of House.
"WHAT?!?" McGonagall was horrified. "Why didn't you tell me, Mr. Potter?"
"Why would I? You told me to keep my head down, Ma'am. There was no reason to tell you." Harry replied so matter of factly, that Minerva's heart broke.
"You poor child. I've failed you, haven't I?" Minerva McGonagall quickly recovered her composure then turned to the room at large. She pointed to her throat and said Sonorus. She then called all of Gryffindor House down to the Common Room.
She found the other students with scarred hands, then ran off to speak to the Ministry. She wasn't letting Albus get in her way. Due to her dilligence, Madame Umbridge was put to trial, before the entire Wizengamot, for her torture of the students.
After they questioned her under Veritaserum, Umbridge not only admitted to using the blood quill, supposedly under Ministry sanction, but to setting the Dementors on Harry Potter during the previous summer. Cornelius Fudge, seeing that he was really going to be under fire for this, tried to mitigate the damage by asking for the harshest sentence.
After all of this, the professors were all grouped around the headmaster, when Severus Snape noticed Potter, the two youngest Weasleys, Granger, Longbottom and Lovegood all huddled together. Hermione (when did he start thinking of her like that?) was laughing and gesturing, apparently amusing the others.
Severus turned back to the headmaster just in time to hear "...and without Miss Granger's question, we would never have been able to get rid of Madame Umbridge so decisively. She was also quite ingenious in her method of getting her out to the Centaurs."
Severus thought to himself that Hermione was also quite ruthless. He rather admired her for it. He smiled to himself, although it must have showed on his face in a quirk of his lip, because it resulted in a couple of frightened Hufflepuffs.
