Harry did not realize how much of a threat Sirius Black posed, until the night he infiltrated the castle. Harry was under the illusion that Sirius Black cannot reach him here- in Hogwarts. He was wrong.
Harry realized that he knows very little about Sirius Black. Almost nothing. He knows literally two things: he's a Death Eater, and he's a mass murderer. That's it.
He needs to know more. So, Harry, Hermione, and Draco hit the library archives.
"He's very handsome," noted Draco, holding an article from the Daily Prophet featuring a picture of young Sirius.
"He's a mass murderer." Hermione reminded him.
"Right." Draco dropped it over a pile, and moved to the next issue of the Daily Prophet in the archive.
"Peter Pettigrew," Harry read aloud. Both Hermione and Draco turned towards him. "He's one of the thirteen people Black killed, but he's the only one mentioned in name in this article."
Harry put it in the same pile as Draco's article.
They kept looking through old newspapers, but there isn't much about Sirius Black other than the murder of thirteen innocent people, including Peter Pettigrew.
"I found something!" Hermione exclaimed, both Harry and Draco ran towards her. "Oh wait, never mind."
"What is it, Hermione?" Asked Harry.
"It's the wrong Black." Hermione handed him an article titled "Black Death: The House of Black Loses a Son."
"Regulus Arcturus Black died under mysterious circumstances," Draco read out loud.
"He has a dead brother. It's one more thing we know about him now." Harry said, encouragingly, and added the article to the pile of useful articles.
They kept reading and looking for more things, but they couldn't find what they were looking for.
A few hours have passed, and it was almost curfew.
Hermione has passed out, using the irrelevant pile of articles as a pillow. Draco was yawning, which, in turn, was making Harry yawn as well.
"This is not helpful." Draco stated.
"Agreed." Harry said, and looked around him, "but it's all we have, I guess."
"Not really."
Hermione headed to the Ravenclaw tower.
Harry and Draco walked in the direction of the Slytherin dungeons, but took a turn along the way.
"Wait wait," Draco stopped, and so did Harry. "The cloak." Draco said, and Harry pulled out of his bag.
Under the cloak, they made their way to Filch's office. The door was open, but Filch wasn't there. He was probably patrolling the hallways, looking for students out after the curfew. Like them two.
The slowly snuck in, and looked around for…
"The keys!" Harry exclaimed, whispering.
"Shush!"
"Sorry."
They stole the keys, and made their way to the archives. While Harry had never been there up to that moment, Draco spent many detentions in this room.
"Okay, so we're looking for Sirius Black," said Draco.
"Maybe also Peter Pettigrew or even Regulus Black."
The two of them got to work.
It wasn't long before they found many records of both Sirius Black and Peter Pettigrew. Very often together and, surprisingly, with professor Lupin and James Potter.
"I'm confused." Harry was confused.
For starters, professor Lupin never mentioned either Pettigrew or Black when he discussed his friendship with Harry's parents with Harry. He's been omitting them, but why?
He also couldn't fathom his father being friends with a Death Eater. Something must've gone horribly wrong. And, how did Black and Pettigrew go from being friends to one killing the other?
Poor Pettigrew.
Harry and Draco kept on reading files, and sorting them, keeping what they deemed relevant, and returned what they didn't need.
By the time the sun went up, they were still there. Harry still reading through the records, and Draco passed out on the floor. He looks very peaceful when he's sleeping.
Harry takes off his cloak and covers Draco with it, like a blanket. So he's warm.