Harry had read all books on magical debts before deciding he didn't owe a life debt to anyone as he didn't feel a pull on his core to go above and beyond what was normal for him.
Not for the sake of the old man or for anyone else. It was from them though that Harry had come to realize Hermione Granger did owe him just such a debt as he had definitely placed himself in peril to rescue her from a Troll on Halloween.
.....
His second year had been another game for Dumbledore. Another testing of Harry's mettle and will to protect. Only this time he was also being tested to see how well he could stand alone against the tide and, if he had a connection to Lord Voldemort, how deep did that connection go? Because, unknown to Harry, Hermione and Ron had told the old man how Harry's scar would bother him any time he was near Voldemort. What was the source of the connection and how greatly did the connection influence Harry's thinking and personality. After all, Dumbledore had tagged Harry to be his weapon of choice in this turf war he was having against Voldemort for control of the playground. The playground in question being the British Wizarding society.
Unfortunately, Harry had once again not realized how his two so-called friends were being used to guide him and reporting back to the Headmaster with every little tidbit of information they could gather for him. Information that he could then use to further manipulate Harry into doing his bidding whether or not it was in Harry's best interest or not. In fact, it was most often decidedly not in Harry's best interest.
It was a year that resulted in a confirmation of the debt between him and Hermione Granger, a new debt between him and Ginerva Weasely being formed, a dead basilisk and a destroyed horocrux in the form of an old diary. Oh and a very grateful freed house-elf devoted to Harry for the gift of his freedom.
But because he could speak to snakes, it had been a lonely year for Harry when the entire school had openly turned against him, isolating and shunning him for not living up to their expectations as the hero they'd always been told he was. All for saving a Hufflepuff boy from a very nasty and painful death by snake bite. After all, the students thought they knew everything about him because they'd grown up hearing wonderful bedtime stories of his fabulous life and not one of those stories had ever said he could talk to snakes. A talent they had been taught was evil. Something only the darkest of witches and wizards possessed or would dare to use in public.
He'd thought Hermione incredibly brave to buck the system, even if she wasn't doing it openly, to help him prove he wasn't the Heir of Slytherin or the one endangering the muggleborn and half blood students. She'd slunk through the halls on a mission to find the proof he needed and discover exactly what the true nature of the threat against the students was as well as where the location of the Chamber of Secrets actually was. He'd even thought she'd committed a couple of crimes by destroying a library book and brewing a complicated potion illegally to help him out. He'd been so stupid. So gullible.
Now he knew it wasn't true but he should've known it then, too. The library was like a cathedral to her. A holy place. No way would she have vandalized a book belonging to the library. She went on frequent rants any time she saw a student writing in the margins of their own bought and paid for books. So he should've realized at the time she'd never destroy one by tearing out a page. Books were her bible and yet he thought she'd torn a page out of one because it contained the information he needed to ride to the rescue. But that, like the stealing of potion ingredients to brew a potion she had no reason to know even existed, had been a carefully planted lie. Hell, even her claiming to be able to brew said potion was nothing more than a lie and a smokescreen.
She had been slinking through the halls as he had thought she was. But she wasn't looking for proof that he wasn't the one endangering the students. She already knew he wasn't. She was looking for the location of the entrance to the Chambers. That was the only true thing she'd told him. She was looking for it because Dumbledore had told her Harry needed to go there and face his destiny. And how could she make sure he went when she didn't know where it was?
But she'd also used those sneaking expeditions to spread the rumors about him trashing his reputation and causing their fellow students to look at him with suspicion and unease. Thereby, making sure the student body remained wary of him. Dumbledore didn't want Harry's naturally quiet and retiring personality swaying the children back to neutrality too soon. Neutrality that would quickly turn to adoration again because really speaking to snakes wasn't all that bad if no one got hurt by it. And so far no one had. Even the dimmest student knew that much. So she kept their mistrust alive with the careful spreading of rumors just as Ronald did with his wary attitude towards, and later lies about, Harry.
As for the supposed crime, well she hadn't done that, either. She'd been given the boomslag skin she'd needed for the advanced potion she'd decided they needed to make so they could find out more about the true Heir of Slytherin. And she was helped in the brewing of the actual potion because there was no way someone who had only been brewing potions for less than one calendar year could've brewed that very complicated potion at all. Let alone in a damp bathroom while still attending all their classes and trying to keep it a secret that they were doing so. Even the most talented beginner brewers would've messed it up. And good as she was at the time, she was only a beginner brewer.
Yet her brew had turned out perfect. Well, except for her supposedly using a cat hair instead of a human one. Which was only further proof that she didn't brew the potion at all. After all, if she could brew a complicated potion like the Polyjuice perfectly the first time she ever tried it, why then would she mistake a feline hair for a human one? Even Harry wouldn't have made that mistake.